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VulnerabilityPublished Updated

CVE-2026-31657: Linux kernel · batman-adv: hold claim backbone gateways by reference

Affects Linux kernelSource CVE Database V5

0

Not known to be exploited · CVSS 9.8 Critical · fixed in f4858832ddef2f39f21e30b7226bbcd3c4b2bc96 : patch Linux kernel as a priority.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 3.1 base score
9.8Critical
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 33% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers can reliably automate steps 1–4 of the kill chain
Technical impact
Total control over the software or total information disclosure

CISA SSVC assessment, 2026-10-16.

Patch
Available – fixed in f4858832ddef2f39f21e30b7226bbcd3c4b2bc96, 7962b522222628596ca9ecc8722efc95367aadbd, 5202f071b367ffbc8e279fc7a00db14f5e587f52 +5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 24 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ 23721387c409087fd3b97e274f34d3ddc0970b74, < f4858832ddef2f39f21e30b7226bbcd3c4b2bc96
Fixed in
  • f4858832ddef2f39f21e30b7226bbcd3c4b2bc96
LinuxLinuxAffected
  • ≥ 23721387c409087fd3b97e274f34d3ddc0970b74, < 7962b522222628596ca9ecc8722efc95367aadbd
Fixed in
  • 7962b522222628596ca9ecc8722efc95367aadbd
LinuxLinuxAffected
  • ≥ 23721387c409087fd3b97e274f34d3ddc0970b74, < 5202f071b367ffbc8e279fc7a00db14f5e587f52
Fixed in
  • 5202f071b367ffbc8e279fc7a00db14f5e587f52
LinuxLinuxAffected
  • ≥ 23721387c409087fd3b97e274f34d3ddc0970b74, < 82d8701b2c930d0e96b0dbc9115a218d791cb0d2
Fixed in
  • 82d8701b2c930d0e96b0dbc9115a218d791cb0d2
LinuxLinuxAffected
  • ≥ 23721387c409087fd3b97e274f34d3ddc0970b74, < 69d1ce9c72eca91203ffdb8d08bacd511100aec6
Fixed in
  • 69d1ce9c72eca91203ffdb8d08bacd511100aec6
LinuxLinuxAffected
  • ≥ 23721387c409087fd3b97e274f34d3ddc0970b74, < 4dee4c0688443aaf5bbec74aa203c851d1d53c35
Fixed in
  • 4dee4c0688443aaf5bbec74aa203c851d1d53c35

AI-suggested

A fix is available and has been applied in the Linux kernel. Users and administrators should update to the fixed kernel versions identified by the commits listed in establishedFacts.fixedVersions. No additional mitigation steps are indicated beyond applying the official patch.

Description

CVE-2026-31657 is a critical use-after-free vulnerability in the Linux kernel's batman-adv module. The issue arises because the function batadv_bla_add_claim() can replace a claim's backbone gateway pointer and drop the old gateway's last reference while other readers still access it. This leads to unsafe dereferencing of freed memory. The vulnerability has been fixed by ensuring stable references to backbone gateways during read operations.

References

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