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Fencer Vulns
high 8.2

CVE-2026-43233 json

netfilter: nf_conntrack_h323: fix OOB read in decode_choice()

published 2026-05-06 6 mo ago modified 2026-10-19 20 d ago also EUVD-2026-27794

cvss
8.2
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 40%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_conntrack_h323: fix OOB read in decode_choice()

In decode_choice(), the boundary check before get_len() uses the variable `len`, which is still 0 from its initialization at the top of the function:

unsigned int type, ext, len = 0; ... if (ext || (son->attr & OPEN)) { BYTE_ALIGN(bs); if (nf_h323_error_boundary(bs, len, 0)) /* len is 0 here */ return H323_ERROR_BOUND; len = get_len(bs); /* OOB read */

When the bitstream is exactly consumed (bs->cur == bs->end), the check nf_h323_error_boundary(bs, 0, 0) evaluates to (bs->cur + 0 > bs->end), which is false. The subsequent get_len() call then dereferences *bs->cur++, reading 1 byte past the end of the buffer. If that byte has bit 7 set, get_len() reads a second byte as well.

This can be triggered remotely by sending a crafted Q.931 SETUP message with a User-User Information Element containing exactly 2 bytes of PER-encoded data ({0x08, 0x00}) to port 1720 through a firewall with the nf_conntrack_h323 helper active. The decoder fully consumes the PER buffer before reaching this code path, resulting in a 1-2 byte heap-buffer-overflow read confirmed by AddressSanitizer.

Fix this by checking for 2 bytes (the maximum that get_len() may read) instead of the uninitialized `len`. This matches the pattern used at every other get_len() call site in the same file, where the caller checks for 2 bytes of available data before calling get_len().

Patch / fix

  • Linux Linux 5.10.252, 5.15.202, 6.1.165, 6.6.128, 6.12.75, 6.18.16, 6.19.6, 7.0
  • linux Debian 12 6.1.170-1
  • linux Debian 13 6.12.85-1
  • linux Debian 14 6.19.6-1

debian advisories DEBIAN-CVE-2026-43233

  • linux Ubuntu 22.04 LTS 5.15.0-186.196
  • linux Ubuntu 24.04 LTS 6.8.0-134.134
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1112.119
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1060.63
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1112.122
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1063.69
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1108.114
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1058.64

ubuntu advisories UBUNTU-CVE-2026-43233

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel RHEL 8 4.18.0-553.164.1.el8_10
  • perf RHEL 8 4.18.0-553.164.1.el8_10
  • bpftool RHEL 8 4.18.0-553.164.1.el8_10
  • kernel-core RHEL 8 4.18.0-553.164.1.el8_10
  • kernel-tools RHEL 8 4.18.0-553.164.1.el8_10
  • python3-perf RHEL 8 4.18.0-553.164.1.el8_10
  • kernel-modules RHEL 8 4.18.0-553.164.1.el8_10
  • kernel-zfcpdump RHEL 8 4.18.0-553.164.1.el8_10

red hat advisories RHSA-2026:68531RHSA-2026:68532RHSA-2026:57252

  • kernel-syms SLES 16.0, Linux Micro Extras 6.2, SLES for SAP applications 16.0 6.12.0-160000.36.1
  • kernel-obs-build Linux Micro Extras 6.2 6.12.0-160000.36.1
  • kernel-rt Linux Micro 6.2 6.12.0-160000.36.1
  • kernel-64kb SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.36.1
  • kernel-source SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.36.1
  • kernel-default SLES 16.0, SLE High Availability Extension 16.0, Linux Micro 6.2 +1 more 6.12.0-160000.36.1
  • kernel-default-base SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.36.1.160000.2.17
  • kernel-azure SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.36.1

suse advisories SUSE-SU-2026:22742-1SUSE-SU-2026:22769-1SUSE-SU-2026:22835-1SUSE-SU-2026:22812-1SUSE-SU-2026:2914-1SUSE-SU-2026:2800-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.36.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.36.1

opensuse advisories openSUSE-SU-2026:21388-1

  • kernel AlmaLinux 8 4.18.0-553.164.1.el8_10
  • perf AlmaLinux 8 4.18.0-553.164.1.el8_10
  • bpftool AlmaLinux 8 4.18.0-553.164.1.el8_10
  • kernel-core AlmaLinux 8 4.18.0-553.164.1.el8_10
  • kernel-tools AlmaLinux 8 4.18.0-553.164.1.el8_10
  • python3-perf AlmaLinux 8 4.18.0-553.164.1.el8_10
  • kernel-modules AlmaLinux 8 4.18.0-553.164.1.el8_10
  • kernel-zfcpdump AlmaLinux 8 4.18.0-553.164.1.el8_10

almalinux advisories ALSA-2026:68531ALSA-2026:68532ALSA-2026:57252

  • kernel-rt Rocky Linux 8 4.18.0-553.164.1.rt7.505.el8_10
  • kernel Rocky Linux 8 4.18.0-553.164.1.el8_10
  • kernel Rocky Linux 9 5.14.0-687.41.1.el9_8

rocky linux advisories RLSA-2026:68532RLSA-2026:68531RLSA-2026:57252

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-43233 updated cvss 7.0

kernel: netfilter: nf_conntrack_h323: fix OOB read in decode_choice()

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 9 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +12 more Red Hat Enterprise Linux 10 kernel
    affected: no fix available
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-687.41.1.el9_8, perf 5.14.0-687.41.1.el9_8, rtla 5.14.0-687.41.1.el9_8, python3-perf 5.14.0-687.41.1.el9_8, kernel-devel-matched 5.14.0-687.41.1.el9_8, kernel-64k-devel-matched 5.14.0-687.41.1.el9_8, +7 more
    fixed: vendor fix RHSA-2026:57252
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.164.1.el8_10, kernel 4.18.0-553.164.1.el8_10, bpftool 4.18.0-553.164.1.el8_10, kernel-core 4.18.0-553.164.1.el8_10, kernel-tools 4.18.0-553.164.1.el8_10, python3-perf 4.18.0-553.164.1.el8_10, +15 more
    fixed: vendor fix RHSA-2026:68531
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-687.41.1.el9_8, kernel-64k 5.14.0-687.41.1.el9_8, kernel-core 5.14.0-687.41.1.el9_8, kernel-tools 5.14.0-687.41.1.el9_8, kernel-modules 5.14.0-687.41.1.el9_8, kernel-64k-core 5.14.0-687.41.1.el9_8, +27 more Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-687.41.1.el9_8, kernel-debuginfo-common-s390x 5.14.0-687.41.1.el9_8, kernel-debuginfo-common-x86_64 5.14.0-687.41.1.el9_8, kernel-debuginfo-common-aarch64 5.14.0-687.41.1.el9_8, kernel-debuginfo-common-ppc64le 5.14.0-687.41.1.el9_8
    fixed: vendor fix RHSA-2026:57252
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.164.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.164.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.164.1.el8_10
    fixed: vendor fix RHSA-2026:68531
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.164.1.rt7.505.el8_10, kernel-rt-kvm 4.18.0-553.164.1.rt7.505.el8_10, kernel-rt-core 4.18.0-553.164.1.rt7.505.el8_10, kernel-rt-modules 4.18.0-553.164.1.rt7.505.el8_10, kernel-rt-debug-kvm 4.18.0-553.164.1.rt7.505.el8_10, kernel-rt-debug-core 4.18.0-553.164.1.rt7.505.el8_10, +4 more
    fixed: vendor fix RHSA-2026:68532
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-687.41.1.el9_8, kernel-rt-64k 5.14.0-687.41.1.el9_8, kernel-rt-core 5.14.0-687.41.1.el9_8, kernel-rt-modules 5.14.0-687.41.1.el9_8, kernel-rt-64k-core 5.14.0-687.41.1.el9_8, kernel-rt-debug-core 5.14.0-687.41.1.el9_8, +14 more Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-687.41.1.el9_8, kernel-rt-core 5.14.0-687.41.1.el9_8, kernel-rt-modules 5.14.0-687.41.1.el9_8, kernel-rt-debug-core 5.14.0-687.41.1.el9_8, kernel-rt-modules-core 5.14.0-687.41.1.el9_8, kernel-rt-debug-modules 5.14.0-687.41.1.el9_8, +4 more
    fixed: vendor fix RHSA-2026:57252
show 2 more
  • Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.164.1.rt7.505.el8_10, kernel-rt-core 4.18.0-553.164.1.rt7.505.el8_10, kernel-rt-modules 4.18.0-553.164.1.rt7.505.el8_10, kernel-rt-debug-core 4.18.0-553.164.1.rt7.505.el8_10, kernel-rt-debug-modules 4.18.0-553.164.1.rt7.505.el8_10, kernel-rt-modules-extra 4.18.0-553.164.1.rt7.505.el8_10, +2 more
    fixed: vendor fix RHSA-2026:68532
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
23 d ago

Exploit prediction

0.46% chance of exploitation in the next 30 days, higher than 40% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

Affected products

  • Linux Linux

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.