# CVE-2026-31427: netfilter: nf_conntrack_sip: fix use of uninitialized rtp_addr in process_sdp

> An attacker can cause the Linux kernel to leak stack memory or corrupt SIP session data by sending crafted SDP packets with no active media lines.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 13 Apr 2026
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-82709, BELL-CVE-2026-31427, DEBIAN-CVE-2026-31427, GHSA-w9rr-8fx7-936w, ROOT-OS-DEBIAN-11-CVE-2026-31427, ROOT-OS-DEBIAN-12-CVE-2026-31427, ROOT-OS-DEBIAN-13-CVE-2026-31427, ROOT-OS-UBUNTU-2204-CVE-2026-31427, ROOT-OS-UBUNTU-2404-CVE-2026-31427, UBUNTU-CVE-2026-31427

## What is CVE-2026-31427?

CVE-2026-31427 is a medium-severity vulnerability in Linux kernel, published on 13 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

Weakness: CWE-908 (Use of Uninitialized Resource)

## Which versions are affected by CVE-2026-31427?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31427?

Apply the vendor's patch.

## Is CVE-2026-31427 being exploited?

There is no known exploitation of CVE-2026-31427 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31427 and fix it if it is affected.

What it is: CVE-2026-31427 is a medium-severity vulnerability in Linux kernel, published on 13 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-31427 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-31427/ (Markdown: https://insights.sbomify.com/CVE-2026-31427/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31427
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31427
- OSV: https://osv.dev/vulnerability/CVE-2026-31427

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31427/
Summaries are generated and may contain mistakes; the official description above is the record.