---
id: CVE-2026-31427
title: 'netfilter: nf_conntrack_sip: fix use of uninitialized rtp_addr in process_sdp'
summary: |-
  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_n…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 <
    faa6ea32797a1847790514ff0da1be1d09771580
  - >-
    Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 <
    82baeb871e8f04906bc886273fdf0209e1754eb3
  - >-
    Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 <
    6e5e3c87b7e6212f1d8414fc2e4d158b01e12025
  - >-
    Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 <
    fe463e76c9b4b0b43b5ee8961b4c500231f1a3f6
  - >-
    Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 <
    7edca70751b9bdb5b83eed53cde21eccf3c86147
  - >-
    Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 <
    01f34a80ac23ae90b1909b94b4ed05343a62f646
  - >-
    Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 <
    52fdda318ef2362fc5936385bcb8b3d0328ee629
  - >-
    Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 <
    6a2b724460cb67caed500c508c2ae5cf012e4db4
  - Linux 2.6.26
published: '2026-04-13'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:47:03.009Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-31427'
references:
  - url: 'https://git.kernel.org/stable/c/faa6ea32797a1847790514ff0da1be1d09771580'
  - url: 'https://git.kernel.org/stable/c/82baeb871e8f04906bc886273fdf0209e1754eb3'
  - url: 'https://git.kernel.org/stable/c/6e5e3c87b7e6212f1d8414fc2e4d158b01e12025'
  - url: 'https://git.kernel.org/stable/c/fe463e76c9b4b0b43b5ee8961b4c500231f1a3f6'
  - url: 'https://git.kernel.org/stable/c/7edca70751b9bdb5b83eed53cde21eccf3c86147'
  - url: 'https://git.kernel.org/stable/c/01f34a80ac23ae90b1909b94b4ed05343a62f646'
  - url: 'https://git.kernel.org/stable/c/52fdda318ef2362fc5936385bcb8b3d0328ee629'
  - url: 'https://git.kernel.org/stable/c/6a2b724460cb67caed500c508c2ae5cf012e4db4'
tags:
  - cve.org
epss: 0.00171
epssPercentile: 0.05673
ingestedAt: '2026-09-08T15:33:26.990Z'
---

## Overview

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.

## Affected

- `Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < faa6ea32797a1847790514ff0da1be1d09771580`
- `Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < 82baeb871e8f04906bc886273fdf0209e1754eb3`
- `Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < 6e5e3c87b7e6212f1d8414fc2e4d158b01e12025`
- `Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < fe463e76c9b4b0b43b5ee8961b4c500231f1a3f6`
- `Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < 7edca70751b9bdb5b83eed53cde21eccf3c86147`
- `Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < 01f34a80ac23ae90b1909b94b4ed05343a62f646`
- `Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < 52fdda318ef2362fc5936385bcb8b3d0328ee629`
- `Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < 6a2b724460cb67caed500c508c2ae5cf012e4db4`
- `Linux 2.6.26`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.