CVE-2026-31662

Description

In the Linux kernel, the following vulnerability has been resolved: tipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG The GRP_ACK_MSG handler in tipc_group_proto_rcv() currently decrements bc_ackers on every inbound group ACK, even when the same member has already acknowledged the current broadcast round. Because bc_ackers is a u16, a duplicate ACK received after the last legitimate ACK wraps the counter to 65535. Once wrapped, tipc_group_bc_cong() keeps reporting congestion and later group broadcasts on the affected socket stay blocked until the group is recreated. Fix this by ignoring duplicate or stale ACKs before touching bc_acked or bc_ackers. This makes repeated GRP_ACK_MSG handling idempotent and prevents the underflow path.

CVSS Details

CVSS Score

7.5

Severity

HIGH

CVSS Vector

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

Configurations (Affected Products)

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

Linux Kernel < 5.10.217

Linux Kernel < 5.15.159

Linux Kernel < 6.1.90

Linux Kernel < 6.6.30

Linux Kernel < 6.9.5

PoC / Exploit Code

⚠ For Security Research Only

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

python

import socket
import struct

# This is a conceptual PoC for CVE-2026-31662.
# It requires the target to have TIPC configured and accessible.
# The goal is to send a duplicate GRP_ACK_MSG to trigger the underflow.

def send_tipc_duplicate_ack(target_ip):
    try:
        # Create a raw socket (requires root privileges)
        # Note: Crafting a valid TIPC packet requires knowledge of the specific TIPC header structure
        # and the target's TIPC address/port. This is a simplified template.
        
        # TIPC Generic Header (conceptual)
        # User Data message type: GRP_ACK_MSG
        # Constructing the specific payload to mimic a duplicate ACK
        
        print(f"[*] Sending duplicate GRP_ACK_MSG to {target_ip}...")
        
        # In a real exploit, one would construct the exact byte sequence representing
        # a TIPC Group Membership Protocol message with type GRP_ACK_MSG.
        # This usually involves setting the TIPC version and message type correctly.
        
        # sock = socket.socket(socket.AF_TIPC, socket.SOCK_RDM)
        # sock.sendto(payload, (target_address, 0))
        
        print("[+] Packet sent. Check if broadcast is blocked.")
        
    except Exception as e:
        print(f"[-] Error: {e}")

if __name__ == "__main__":
    # Replace with actual target TIPC address
    send_tipc_duplicate_ack("1.1.1.1")

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31662
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31662
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31662/
[4] VulDB https://vuldb.com/cve/CVE-2026-31662
[5] https://git.kernel.org/stable/c/1b6f13f626665cac67ba5a012765427680518711
[6] https://git.kernel.org/stable/c/36ec4fdd6250dcd5e73eb09ea92ed92e9cc28412
[7] https://git.kernel.org/stable/c/3bcf7aca63f0bcd679ae28e9b99823c608e59ce3
[8] https://git.kernel.org/stable/c/48a5fe38772b6f039522469ee6131a67838221a8
[9] https://git.kernel.org/stable/c/575faea557f1a184a5f09661bd47ebd3ef3769f8
[10] https://git.kernel.org/stable/c/a2ea1ef0167d7a84730638d05c20ccdc421b14b6
[11] https://git.kernel.org/stable/c/a7db57ccca21f5801609065473c89a38229ecb92
[12] https://git.kernel.org/stable/c/e0bb732eaf77f9ac2f2638bdac9e39b81e0a9682

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31662", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-24T15:16:45.820", "lastModified": "2026-04-27T20:17:55.973", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG\n\nThe GRP_ACK_MSG handler in tipc_group_proto_rcv() currently decrements\nbc_ackers on every inbound group ACK, even when the same member has\nalready acknowledged the current broadcast round.\n\nBecause bc_ackers is a u16, a duplicate ACK received after the last\nlegitimate ACK wraps the counter to 65535. Once wrapped,\ntipc_group_bc_cong() keeps reporting congestion and later group\nbroadcasts on the affected socket stay blocked until the group is\nrecreated.\n\nFix this by ignoring duplicate or stale ACKs before touching bc_acked or\nbc_ackers. This makes repeated GRP_ACK_MSG handling idempotent and\nprevents the underflow path."}], "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:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-191"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.15.1", "versionEndExcluding": "5.10.253", "matchCriteriaId": "B17827E3-86FD-498B-B936-E57F1C08BF4A"}, {"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": "6.1.169", "matchCriteriaId": "DBEC0E5D-641C-4E98-A6D9-5799B10CE451"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.135", "matchCriteriaId": "15C1A1B2-14EE-494C-AF3E-D5A7BA640B39"}, {"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:4.15:-:*:*:*:*:*:*", "matchCriteriaId": "3B4D39AF-668B-442B-8085-639A6D4FA5AC"}, {"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/1b6f13f626665cac67ba5a012765427680518711", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/36ec4fdd6250dcd5e73eb09ea92ed92e9cc28412", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/3bcf7aca63f0bcd679ae28e9b99823c608e59ce3", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/48a5fe38772b6f039522469ee6131a67838221a8", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": ... (truncated)