CVE-2026-31657: Linux kernel · batman-adv: hold claim backbone gateways by reference
Affects Linux kernelSource CVE Database V5
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
- 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:HExploitation evidence
Disclosed: evidence found.
CVE published 24 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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
| Product | Affected | Fixed in |
|---|---|---|
| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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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
- git.kernel.org/stable/c/5202f071b367ffbc8e279fc7a00db14f5e587f52 (opens in a new tab)
- git.kernel.org/stable/c/69d1ce9c72eca91203ffdb8d08bacd511100aec6 (opens in a new tab)
- git.kernel.org/stable/c/f4858832ddef2f39f21e30b7226bbcd3c4b2bc96 (opens in a new tab)
- git.kernel.org/stable/c/2f55b58b5a0bbed192d60c444a45a49cdf1b545f (opens in a new tab)
- git.kernel.org/stable/c/7962b522222628596ca9ecc8722efc95367aadbd (opens in a new tab)
- git.kernel.org/stable/c/4dee4c0688443aaf5bbec74aa203c851d1d53c35 (opens in a new tab)
- git.kernel.org/stable/c/1f2dc36c297d27733f1b380ea644cf15a361bd7b (opens in a new tab)
- git.kernel.org/stable/c/82d8701b2c930d0e96b0dbc9115a218d791cb0d2 (opens in a new tab)