CVE-2026-63981: Linux kernel · net/sched: act_mirred: Fix blockcast recursion bypass leading to stack overflow
Affects Linux kernelSource GCVE Database
Not known to be exploited.
Data as of 12 Nov 2026, 18:21 UTC
Rated High by Threat Radar's AI analysis · No CVSS score from NVD or the CNA
Thin evidence
One scorer or noneExploitation evidence
Disclosed: evidence found.
CVE published 19 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 12 Nov 2026.
What to do
AI-suggested
A fix is available that properly increments and decrements the recursion counter around the tcf_blockcast() call to enforce the recursion limit and prevent stack overflow. Users should apply the official Linux kernel patch that addresses this issue. No other mitigation is indicated.
Description
A stack overflow vulnerability exists in the Linux kernel's net/sched subsystem due to a recursion counter bypass in the act_mirred module when using blockcast. This flaw allows unbounded recursion between two devices sharing a TC egress block with mirred blockcast rules, leading to kernel stack overflow and potential kernel panic. The issue is exploitable by unprivileged users with network namespace capabilities.