Medium 5.5Published Apr 13, 2026

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

Updated under an hour ago (Oct 27, 2026, 9:50 AM ET)

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Exploited in the last 30 days

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.

CVSS: 5.5 MEDIUM (v3.1, NVD)CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE): Not given
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: Linux
NVD analysis: Modified
Record last updated: Oct 14, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Linux Linux linux:linux (from the name)	from 4ab9e64e5e3c0516577818804aaf13a630d67bc9 before faa6ea32797a1847790514ff0da1be1d09771580; from 4ab9e64e5e3c0516577818804aaf13a630d67bc9 before 82baeb871e8f04906bc886273fdf0209e1754eb3; from 4ab9e64e5e3c0516577818804aaf13a630d67bc9 before 6e5e3c87b7e6212f1d8414fc2e4d158b01e12025; from 4ab9e64e5e3c0516577818804aaf13a630d67bc9 before fe463e76c9b4b0b43b5ee8961b4c500231f1a3f6; from 4ab9e64e5e3c0516577818804aaf13a630d67bc9 before 7edca70751b9bdb5b83eed53cde21eccf3c86147; 4ab9e64e5e3c0516577818804aaf13a630d67bc9 builds before 01f34a80ac23ae90b1909b94b4ed05343a62f646; from 4ab9e64e5e3c0516577818804aaf13a630d67bc9 before 52fdda318ef2362fc5936385bcb8b3d0328ee629; from 4ab9e64e5e3c0516577818804aaf13a630d67bc9 before 6a2b724460cb67caed500c508c2ae5cf012e4db4	CNA record
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518_4_pn_dp_mfp (from the name)	from V3.1.6	CISA ADP
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518f_4_pn_dp_mfp (from the name)	from V3.1.6	CISA ADP
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP siemens:siplus_s7_1500_cpu_1518_4_pn_dp_mfp (from the name)	from V3.1.6	CISA ADP
linux linux_kernel linux:linux_kernel	from 2.6.26 before 5.10.253; from 5.11 before 5.15.203; from 5.16 before 6.1.168; from 6.2 before 6.6.131; from 6.7 before 6.12.80; from 6.13 before 6.18.21; from 6.19 before 6.19.11; 7.0; and 4 more ranges	NVD

References

References

https://git.kernel.org/stable/c/faa6ea32797a1847790514ff0da1be1d09771580	patch
https://git.kernel.org/stable/c/82baeb871e8f04906bc886273fdf0209e1754eb3	patch
https://git.kernel.org/stable/c/6e5e3c87b7e6212f1d8414fc2e4d158b01e12025	patch
https://git.kernel.org/stable/c/fe463e76c9b4b0b43b5ee8961b4c500231f1a3f6	patch
https://git.kernel.org/stable/c/7edca70751b9bdb5b83eed53cde21eccf3c86147	patch
https://git.kernel.org/stable/c/01f34a80ac23ae90b1909b94b4ed05343a62f646	patch
https://git.kernel.org/stable/c/52fdda318ef2362fc5936385bcb8b3d0328ee629	patch
https://git.kernel.org/stable/c/6a2b724460cb67caed500c508c2ae5cf012e4db4	patch
https://cert-portal.siemens.com/productcert/html/ssa-019113.html
https://cert-portal.siemens.com/productcert/html/ssa-082556.html
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The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.