ID

VAR-201906-1175

CVE

CVE-2019-11477

TITLE

Linux Kernel  Integer overflow vulnerability in

DESCRIPTION

Jonathan Looney discovered that the TCP_SKB_CB(skb)->tcp_gso_segs value was subject to an integer overflow in the Linux kernel when handling TCP Selective Acknowledgments (SACKs). A remote attacker could use this to cause a denial of service. This has been fixed in stable kernel releases 4.4.182, 4.9.182, 4.14.127, 4.19.52, 5.1.11, and is fixed in commit 3b4929f65b0d8249f19a50245cd88ed1a2f78cff. Linux Kernel Exists in an integer overflow vulnerability.Service operation interruption (DoS) It may be in a state. ========================================================================== Kernel Live Patch Security Notice 0058-1 October 22, 2019 linux vulnerability ========================================================================== A security issue affects these releases of Ubuntu: | Series | Base kernel | Arch | flavors | |------------------+--------------+----------+------------------| | Ubuntu 18.04 LTS | 4.15.0 | amd64 | aws | | Ubuntu 18.04 LTS | 4.15.0 | amd64 | generic | | Ubuntu 18.04 LTS | 4.15.0 | amd64 | lowlatency | | Ubuntu 18.04 LTS | 4.15.0 | amd64 | oem | | Ubuntu 18.04 LTS | 5.0.0 | amd64 | azure | | Ubuntu 14.04 LTS | 4.4.0 | amd64 | generic | | Ubuntu 14.04 LTS | 4.4.0 | amd64 | lowlatency | | Ubuntu 16.04 LTS | 4.4.0 | amd64 | aws | | Ubuntu 16.04 LTS | 4.4.0 | amd64 | generic | | Ubuntu 16.04 LTS | 4.4.0 | amd64 | lowlatency | | Ubuntu 16.04 LTS | 4.15.0 | amd64 | azure | | Ubuntu 16.04 LTS | 4.15.0 | amd64 | generic | | Ubuntu 16.04 LTS | 4.15.0 | amd64 | lowlatency | Summary: Several security issues were fixed in the kernel. Software Description: - linux: Linux kernel Details: It was discovered that a race condition existed in the GFS2 file system in the Linux kernel. (CVE-2016-10905) It was discovered that a use-after-free error existed in the block layer subsystem of the Linux kernel when certain failure conditions occurred. (CVE-2018-20856) It was discovered that the USB gadget Midi driver in the Linux kernel contained a double-free vulnerability when handling certain error conditions. (CVE-2018-20961) It was discovered that the XFS file system in the Linux kernel did not properly handle mount failures in some situations. (CVE-2018-20976) It was discovered that the RSI 91x Wi-Fi driver in the Linux kernel did not did not handle detach operations correctly, leading to a use-after-free vulnerability. (CVE-2018-21008) It was discovered that the Intel Wi-Fi device driver in the Linux kernel did not properly validate certain Tunneled Direct Link Setup (TDLS). (CVE-2019-0136) It was discovered that the Linux kernel on ARM processors allowed a tracing process to modify a syscall after a seccomp decision had been made on that syscall. (CVE-2019-2181) It was discovered that the Marvell Wireless LAN device driver in the Linux kernel did not properly validate the BSS descriptor. (CVE-2019-3846) It was discovered that a heap buffer overflow existed in the Marvell Wireless LAN device driver for the Linux kernel. (CVE-2019-10126) It was discovered that the Bluetooth UART implementation in the Linux kernel did not properly check for missing tty operations. (CVE-2019-11478) It was discovered that the ext4 file system implementation in the Linux kernel did not properly zero out memory in some situations. A local attacker could use this to expose sensitive information (kernel memory). (CVE-2019-11833) It was discovered that the PowerPC dlpar implementation in the Linux kernel did not properly check for allocation errors in some situations. (CVE-2019-12614) It was discovered that the floppy driver in the Linux kernel did not properly validate meta data, leading to a buffer overread. (CVE-2019-14283) It was discovered that the floppy driver in the Linux kernel did not properly validate ioctl() calls, leading to a division-by-zero. (CVE-2019-14284) Wen Huang discovered that the Marvell Wi-Fi device driver in the Linux kernel did not properly perform bounds checking, leading to a heap overflow. (CVE-2019-14814) Wen Huang discovered that the Marvell Wi-Fi device driver in the Linux kernel did not properly perform bounds checking, leading to a heap overflow. (CVE-2019-14815) Wen Huang discovered that the Marvell Wi-Fi device driver in the Linux kernel did not properly perform bounds checking, leading to a heap overflow. (CVE-2019-14816) Matt Delco discovered that the KVM hypervisor implementation in the Linux kernel did not properly perform bounds checking when handling coalesced MMIO write operations. (CVE-2019-14835) Update instructions: The problem can be corrected by updating your livepatches to the following versions: | Kernel | Version | flavors | |--------------------------+----------+--------------------------| | 4.4.0-148.174 | 58.1 | lowlatency, generic | | 4.4.0-148.174~14.04.1 | 58.1 | lowlatency, generic | | 4.4.0-150.176 | 58.1 | generic, lowlatency | | 4.4.0-150.176~14.04.1 | 58.1 | lowlatency, generic | | 4.4.0-151.178 | 58.1 | lowlatency, generic | | 4.4.0-151.178~14.04.1 | 58.1 | generic, lowlatency | | 4.4.0-154.181 | 58.1 | lowlatency, generic | | 4.4.0-154.181~14.04.1 | 58.1 | generic, lowlatency | | 4.4.0-157.185 | 58.1 | lowlatency, generic | | 4.4.0-157.185~14.04.1 | 58.1 | generic, lowlatency | | 4.4.0-159.187 | 58.1 | lowlatency, generic | | 4.4.0-159.187~14.04.1 | 58.1 | generic, lowlatency | | 4.4.0-161.189 | 58.1 | lowlatency, generic | | 4.4.0-161.189~14.04.1 | 58.1 | lowlatency, generic | | 4.4.0-164.192 | 58.1 | lowlatency, generic | | 4.4.0-164.192~14.04.1 | 58.1 | lowlatency, generic | | 4.4.0-165.193 | 58.1 | generic, lowlatency | | 4.4.0-1083.93 | 58.1 | aws | | 4.4.0-1084.94 | 58.1 | aws | | 4.4.0-1085.96 | 58.1 | aws | | 4.4.0-1087.98 | 58.1 | aws | | 4.4.0-1088.99 | 58.1 | aws | | 4.4.0-1090.101 | 58.1 | aws | | 4.4.0-1092.103 | 58.1 | aws | | 4.4.0-1094.105 | 58.1 | aws | | 4.15.0-50.54 | 58.1 | generic, lowlatency | | 4.15.0-50.54~16.04.1 | 58.1 | generic, lowlatency | | 4.15.0-51.55 | 58.1 | generic, lowlatency | | 4.15.0-51.55~16.04.1 | 58.1 | generic, lowlatency | | 4.15.0-52.56 | 58.1 | lowlatency, generic | | 4.15.0-52.56~16.04.1 | 58.1 | generic, lowlatency | | 4.15.0-54.58 | 58.1 | generic, lowlatency | | 4.15.0-54.58~16.04.1 | 58.1 | generic, lowlatency | | 4.15.0-55.60 | 58.1 | generic, lowlatency | | 4.15.0-58.64 | 58.1 | generic, lowlatency | | 4.15.0-58.64~16.04.1 | 58.1 | lowlatency, generic | | 4.15.0-60.67 | 58.1 | lowlatency, generic | | 4.15.0-60.67~16.04.1 | 58.1 | generic, lowlatency | | 4.15.0-62.69 | 58.1 | generic, lowlatency | | 4.15.0-62.69~16.04.1 | 58.1 | lowlatency, generic | | 4.15.0-64.73 | 58.1 | generic, lowlatency | | 4.15.0-64.73~16.04.1 | 58.1 | lowlatency, generic | | 4.15.0-65.74 | 58.1 | lowlatency, generic | | 4.15.0-1038.43 | 58.1 | oem | | 4.15.0-1039.41 | 58.1 | aws | | 4.15.0-1039.44 | 58.1 | oem | | 4.15.0-1040.42 | 58.1 | aws | | 4.15.0-1041.43 | 58.1 | aws | | 4.15.0-1043.45 | 58.1 | aws | | 4.15.0-1043.48 | 58.1 | oem | | 4.15.0-1044.46 | 58.1 | aws | | 4.15.0-1045.47 | 58.1 | aws | | 4.15.0-1045.50 | 58.1 | oem | | 4.15.0-1047.49 | 58.1 | aws | | 4.15.0-1047.51 | 58.1 | azure | | 4.15.0-1048.50 | 58.1 | aws | | 4.15.0-1049.54 | 58.1 | azure | | 4.15.0-1050.52 | 58.1 | aws | | 4.15.0-1050.55 | 58.1 | azure | | 4.15.0-1050.57 | 58.1 | oem | | 4.15.0-1051.53 | 58.1 | aws | | 4.15.0-1051.56 | 58.1 | azure | | 4.15.0-1052.57 | 58.1 | azure | | 4.15.0-1055.60 | 58.1 | azure | | 4.15.0-1056.61 | 58.1 | azure | | 4.15.0-1056.65 | 58.1 | oem | | 4.15.0-1057.62 | 58.1 | azure | | 4.15.0-1057.66 | 58.1 | oem | | 4.15.0-1059.64 | 58.1 | azure | | 5.0.0-1014.14~18.04.1 | 58.1 | azure | | 5.0.0-1016.17~18.04.1 | 58.1 | azure | | 5.0.0-1018.19~18.04.1 | 58.1 | azure | | 5.0.0-1020.21~18.04.1 | 58.1 | azure | Support Information: Kernels older than the levels listed below do not receive livepatch updates. Please upgrade your kernel as soon as possible. | Series | Version | Flavors | |------------------+------------------+--------------------------| | Ubuntu 18.04 LTS | 4.15.0-1039 | aws | | Ubuntu 16.04 LTS | 4.4.0-1083 | aws | | Ubuntu 18.04 LTS | 5.0.0-1000 | azure | | Ubuntu 16.04 LTS | 4.15.0-1047 | azure | | Ubuntu 18.04 LTS | 4.15.0-50 | generic lowlatency | | Ubuntu 16.04 LTS | 4.15.0-50 | generic lowlatency | | Ubuntu 14.04 LTS | 4.4.0-148 | generic lowlatency | | Ubuntu 18.04 LTS | 4.15.0-1038 | oem | | Ubuntu 16.04 LTS | 4.4.0-148 | generic lowlatency | References: CVE-2016-10905, CVE-2018-20856, CVE-2018-20961, CVE-2018-20976, CVE-2018-21008, CVE-2019-0136, CVE-2019-2054, CVE-2019-2181, CVE-2019-3846, CVE-2019-10126, CVE-2019-10207, CVE-2019-11477, CVE-2019-11478, CVE-2019-11833, CVE-2019-12614, CVE-2019-14283, CVE-2019-14284, CVE-2019-14814, CVE-2019-14815, CVE-2019-14816, CVE-2019-14821, CVE-2019-14835 -- ubuntu-security-announce mailing list ubuntu-security-announce@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-security-announce . Description: The kernel-rt packages provide the Real Time Linux Kernel, which enables fine-tuning for systems with extremely high determinism requirements. -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 ==================================================================== Red Hat Security Advisory Synopsis: Important: kernel security and bug fix update Advisory ID: RHSA-2019:1485-01 Product: Red Hat Enterprise Linux Advisory URL: https://access.redhat.com/errata/RHSA-2019:1485 Issue date: 2019-06-17 CVE Names: CVE-2019-11477 CVE-2019-11478 CVE-2019-11479 ==================================================================== 1. Summary: An update for kernel is now available for Red Hat Enterprise Linux 7.2 Advanced Update Support, Red Hat Enterprise Linux 7.2 Telco Extended Update Support, and Red Hat Enterprise Linux 7.2 Update Services for SAP Solutions. Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section. 2. Relevant releases/architectures: Red Hat Enterprise Linux Server AUS (v. 7.2) - noarch, x86_64 Red Hat Enterprise Linux Server E4S (v. 7.2) - noarch, x86_64 Red Hat Enterprise Linux Server Optional AUS (v. 7.2) - x86_64 Red Hat Enterprise Linux Server Optional E4S (v. 7.2) - x86_64 Red Hat Enterprise Linux Server Optional TUS (v. 7.2) - x86_64 Red Hat Enterprise Linux Server TUS (v. 7.2) - noarch, x86_64 3. While processing SACK segments, the Linux kernel's socket buffer (SKB) data structure becomes fragmented. To efficiently process SACK blocks, the Linux kernel merges multiple fragmented SKBs into one, potentially overflowing the variable holding the number of segments. A remote attacker could use this flaw to crash the Linux kernel by sending a crafted sequence of SACK segments on a TCP connection with small value of TCP MSS, resulting in a denial of service (DoS). (CVE-2019-11477) * Kernel: tcp: excessive resource consumption while processing SACK blocks allows remote denial of service (CVE-2019-11478) * Kernel: tcp: excessive resource consumption for TCP connections with low MSS allows remote denial of service (CVE-2019-11479) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section. Bug Fix(es): * THP: Race between MADV_DONTNEED and NUMA hinting node migration code (BZ#1698103) * [RHEL7] md_clear flag missing from /proc/cpuinfo on late microcode update (BZ#1712989) * [RHEL7] MDS mitigations are not enabled after double microcode update (BZ#1712994) * WARNING: CPU: 0 PID: 0 at kernel/jump_label.c:90 __static_key_slow_dec+0xa6/0xb0 (BZ#1713000) 4. Solution: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 The system must be rebooted for this update to take effect. 5. Bugs fixed (https://bugzilla.redhat.com/): 1719123 - CVE-2019-11477 Kernel: tcp: integer overflow while processing SACK blocks allows remote denial of service 1719128 - CVE-2019-11478 Kernel: tcp: excessive resource consumption while processing SACK blocks allows remote denial of service 1719129 - CVE-2019-11479 Kernel: tcp: excessive resource consumption for TCP connections with low MSS allows remote denial of service 6. Package List: Red Hat Enterprise Linux Server AUS (v. 7.2): Source: kernel-3.10.0-327.79.2.el7.src.rpm noarch: kernel-abi-whitelists-3.10.0-327.79.2.el7.noarch.rpm kernel-doc-3.10.0-327.79.2.el7.noarch.rpm x86_64: kernel-3.10.0-327.79.2.el7.x86_64.rpm kernel-debug-3.10.0-327.79.2.el7.x86_64.rpm kernel-debug-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-debug-devel-3.10.0-327.79.2.el7.x86_64.rpm kernel-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-debuginfo-common-x86_64-3.10.0-327.79.2.el7.x86_64.rpm kernel-devel-3.10.0-327.79.2.el7.x86_64.rpm kernel-headers-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-libs-3.10.0-327.79.2.el7.x86_64.rpm perf-3.10.0-327.79.2.el7.x86_64.rpm perf-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm python-perf-3.10.0-327.79.2.el7.x86_64.rpm python-perf-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm Red Hat Enterprise Linux Server E4S (v. 7.2): Source: kernel-3.10.0-327.79.2.el7.src.rpm noarch: kernel-abi-whitelists-3.10.0-327.79.2.el7.noarch.rpm kernel-doc-3.10.0-327.79.2.el7.noarch.rpm x86_64: kernel-3.10.0-327.79.2.el7.x86_64.rpm kernel-debug-3.10.0-327.79.2.el7.x86_64.rpm kernel-debug-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-debug-devel-3.10.0-327.79.2.el7.x86_64.rpm kernel-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-debuginfo-common-x86_64-3.10.0-327.79.2.el7.x86_64.rpm kernel-devel-3.10.0-327.79.2.el7.x86_64.rpm kernel-headers-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-libs-3.10.0-327.79.2.el7.x86_64.rpm perf-3.10.0-327.79.2.el7.x86_64.rpm perf-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm python-perf-3.10.0-327.79.2.el7.x86_64.rpm python-perf-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm Red Hat Enterprise Linux Server TUS (v. 7.2): Source: kernel-3.10.0-327.79.2.el7.src.rpm noarch: kernel-abi-whitelists-3.10.0-327.79.2.el7.noarch.rpm kernel-doc-3.10.0-327.79.2.el7.noarch.rpm x86_64: kernel-3.10.0-327.79.2.el7.x86_64.rpm kernel-debug-3.10.0-327.79.2.el7.x86_64.rpm kernel-debug-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-debug-devel-3.10.0-327.79.2.el7.x86_64.rpm kernel-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-debuginfo-common-x86_64-3.10.0-327.79.2.el7.x86_64.rpm kernel-devel-3.10.0-327.79.2.el7.x86_64.rpm kernel-headers-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-libs-3.10.0-327.79.2.el7.x86_64.rpm perf-3.10.0-327.79.2.el7.x86_64.rpm perf-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm python-perf-3.10.0-327.79.2.el7.x86_64.rpm python-perf-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm Red Hat Enterprise Linux Server Optional AUS (v. 7.2): x86_64: kernel-debug-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-debuginfo-common-x86_64-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-libs-devel-3.10.0-327.79.2.el7.x86_64.rpm perf-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm python-perf-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm Red Hat Enterprise Linux Server Optional E4S (v. 7.2): x86_64: kernel-debug-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-debuginfo-common-x86_64-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-libs-devel-3.10.0-327.79.2.el7.x86_64.rpm perf-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm python-perf-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm Red Hat Enterprise Linux Server Optional TUS (v. 7.2): x86_64: kernel-debug-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-debuginfo-common-x86_64-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm kernel-tools-libs-devel-3.10.0-327.79.2.el7.x86_64.rpm perf-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm python-perf-debuginfo-3.10.0-327.79.2.el7.x86_64.rpm These packages are GPG signed by Red Hat for security. Our key and details on how to verify the signature are available from https://access.redhat.com/security/team/key/ 7. References: https://access.redhat.com/security/cve/CVE-2019-11477 https://access.redhat.com/security/cve/CVE-2019-11478 https://access.redhat.com/security/cve/CVE-2019-11479 https://access.redhat.com/security/updates/classification/#important https://access.redhat.com/security/vulnerabilities/tcpsack 8. Contact: The Red Hat security contact is <secalert@redhat.com>. More contact details at https://access.redhat.com/security/team/contact/ Copyright 2019 Red Hat, Inc. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIVAwUBXQfrL9zjgjWX9erEAQh8Yw//XDYZhLE+6/G5jELh43MDCVjixj/y8u2b RaMA/eOCJcq1MXV9k5XDruAeZWoMUcCV3OvBi4NIdQ4GXNb0idp3HvXUbAn6yxjh ANslnVZO8XTYFEpxdSGJf2DLVS+uwe+bnfgQQ6BTFJCDEfOAHsPv/d+jZF3qe2Hm WdD//r+U26C23e6Mz9nu1+k3fyScj+UCYCeIWLikKzboB5TmH1KDH7DS0p71JPKE 65I6b7W1ucj0SdvTpQH7VUesww+TM7KZHHwgo0Ydqusf+RoVyYbW3jbZGb+5m5aB tb8v/zaGsXBthKZmH6LCu02P+0Jbou8vEvqCztuwmqDocAeblm3mzeL8FerKCxCp obEEUcjsTbP+RDkNp2qjlfR6V11msl9PzTHXzrQw+7qxZodE9Jhv8Tvm3uTPvbi6 OTD9ez1Hkw5yaWIJBEitGLMxl4HjHaSXOLwbWkoQcEsv1ENmKtvz6wz64zefxljX VBPkLVuLGdwOzOlXHa9Oks3bWiKYUHt36R5sdz+uYL6NTCL5CLv8oUXCN5bYWRlU lCA6f5EYCR3Em8VFChAA51f+i688hmxq4sJwNtvoMVG96FwtVgSmmikb8cFN9+C+ qLlmaaC+b8cZ9COWfw2XAMkrFCYUNt7eL4W/vlZK+GkiYUxEYFZnJAqLXOWFgVpe nLvixkiNDOA=rUVR -----END PGP SIGNATURE----- -- RHSA-announce mailing list RHSA-announce@redhat.com https://www.redhat.com/mailman/listinfo/rhsa-announce . These packages include redhat-release-virtualization-host, ovirt-node, and rhev-hypervisor. RHVH features a Cockpit user interface for monitoring the host's resources and performing administrative tasks. The following packages have been upgraded to a later upstream version: redhat-release-virtualization-host (4.3.4), redhat-virtualization-host (4.3.4). 7) - aarch64, noarch, ppc64le 3. # Advisory ###### ID: NFLX-2019-001 ###### Title: Linux and FreeBSD Kernel: Multiple TCP-based remote denial of service vulnerabilities ###### Release Date: 2019-06-17 ###### Severity: Critical ### Overview: Netflix has identified several TCP networking vulnerabilities in FreeBSD and Linux kernels. The vulnerabilities specifically relate to the minimum segment size (MSS) and TCP Selective Acknowledgement (SACK) capabilities. The most serious, dubbed _“SACK Panic_,” allows a remotely-triggered kernel panic on recent Linux kernels. There are patches that address most of these vulnerabilities. If patches can not be applied, certain mitigations will be effective. We recommend that affected parties enact one of those described below, based on their environment. __Fix:__ Apply the patch [PATCH_net_1_4.patch](2019-001/PATCH_net_1_4.patch). Additionally, versions of the Linux kernel up to, and including, 4.14 require a second patch [PATCH_net_1a.patch](2019-001/PATCH_net_1a.patch). __Workaround #1:__ Block connections with a low MSS using one of the supplied [filters](2019-001/block-low-mss/README.md). (The values in the filters are examples. You can apply a higher or lower limit, as appropriate for your environment.) Note that these filters may break legitimate connections which rely on a low MSS. Also, note that this mitigation is only effective if TCP probing is disabled (that is, the `net.ipv4.tcp_mtu_probing` sysctl is set to 0, which appears to be the default value for that sysctl). __Workaround #2:__ Disable SACK processing (`/proc/sys/net/ipv4/tcp_sack` set to 0). (Note that either workaround should be sufficient on its own. It is not necessary to apply both workarounds.) ### 2: [CVE-2019-11478](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-11478): SACK Slowness (Linux < 4.15) or Excess Resource Usage (all Linux versions) __Description:__ It is possible to send a crafted sequence of SACKs which will fragment the TCP retransmission queue. On Linux kernels prior to 4.15, an attacker may be able to further exploit the fragmented queue to cause an expensive linked-list walk for subsequent SACKs received for that same TCP connection. __Fix:__ Apply the patch [PATCH_net_2_4.patch](2019-001/PATCH_net_2_4.patch) __Workaround #1:__ Block connections with a low MSS using one of the supplied [filters](2019-001/block-low-mss/README.md). (The values in the filters are examples. You can apply a higher or lower limit, as appropriate for your environment.) Note that these filters may break legitimate connections which rely on a low MSS. Also, note that this mitigation is only effective if TCP probing is disabled (that is, the `net.ipv4.tcp_mtu_probing` sysctl is set to 0, which appears to be the default value for that sysctl). __Workaround #2:__ Disable SACK processing (`/proc/sys/net/ipv4/tcp_sack` set to 0). (Note that either workaround should be sufficient on its own. It is not necessary to apply both workarounds.) ### 3: [CVE-2019-5599](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-5599): SACK Slowness (FreeBSD 12 using the RACK TCP Stack) __Description:__ It is possible to send a crafted sequence of SACKs which will fragment the RACK send map. An attacker may be able to further exploit the fragmented send map to cause an expensive linked-list walk for subsequent SACKs received for that same TCP connection. __Workaround #1:__ Apply the patch [split_limit.patch](2019-001/split_limit.patch) and set the `net.inet.tcp.rack.split_limit` sysctl to a reasonable value to limit the size of the SACK table. __Workaround #2:__ Temporarily disable the RACK TCP stack. (Note that either workaround should be sufficient on its own. It is not necessary to apply both workarounds.) ### 4: [CVE-2019-11479](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-11479): Excess Resource Consumption Due to Low MSS Values (all Linux versions) __Description:__ An attacker can force the Linux kernel to segment its responses into multiple TCP segments, each of which contains only 8 bytes of data. This drastically increases the bandwidth required to deliver the same amount of data. Further, it consumes additional resources (CPU and NIC processing power). This attack requires continued effort from the attacker and the impacts will end shortly after the attacker stops sending traffic. __Fix:__ Two patches [PATCH_net_3_4.patch](2019-001/PATCH_net_3_4.patch) and [PATCH_net_4_4.patch](2019-001/PATCH_net_4_4.patch) add a sysctl which enforces a minimum MSS, set by the `net.ipv4.tcp_min_snd_mss` sysctl. This lets an administrator enforce a minimum MSS appropriate for their applications. __Workaround:__ Block connections with a low MSS using one of the supplied [filters](2019-001/block-low-mss/README.md). (The values in the filters are examples. You can apply a higher or lower limit, as appropriate for your environment.) Note that these filters may break legitimate connections which rely on a low MSS. Also, note that this mitigation is only effective if TCP probing is disabled (that is, the `net.ipv4.tcp_mtu_probing` sysctl is set to 0, which appears to be the default value for that sysctl). ### Note: Good system and application coding and configuration practices (limiting write buffers to the necessary level, monitoring connection memory consumption via SO_MEMINFO, and aggressively closing misbehaving connections) can help to limit the impact of attacks against these kinds of vulnerabilities. ## Acknowledgments: Originally reported by Jonathan Looney. We thank Eric Dumazet for providing Linux fixes and support. We thank Bruce Curtis for providing the Linux filters. We thank Jonathan Lemon and Alexey Kodanev for helping to improve the Linux patches. We gratefully acknowledge the assistance of Tyler Hicks in testing fixes, refining the information about vulnerable versions, and providing assistance during the disclosure process. 6.6) - x86_64 3. Bug Fix(es): * MDS mitigations not enabled on Intel Skylake CPUs (BZ#1713026) * [RHEL6] md_clear flag missing from /proc/cpuinfo (BZ#1713029) * RHEL6 kernel does not disable SMT with mds=full,nosmt (BZ#1713044) 4

AFFECTED PRODUCTS

CVSS

PROBLEMTYPE DATA

THREAT TYPE

local

TYPE

arbitrary

EXPLOIT AVAILABILITY

PATCH

EXTERNAL IDS

REFERENCES

CREDITS

Red Hat

SOURCES

LAST UPDATE DATE

2026-03-04T22:20:11.990000+00:00

SOURCES UPDATE DATE

SOURCES RELEASE DATE