CVE-2026-63825: Linux kernel · gcov: use atomic counter updates to fix concurrent access crashes
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 9.8 Critical · fixed in 7.0.0-1012.12~24.04.1 : patch Linux kernel as a priority.
Data as of 26 Oct 2026, 17:16 UTC
- EPSS
- 0.8% chance of exploitation in 30 days – higher than 56% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 7.0.0-1012.12~24.04.1, 7.0.0-1014.14~24.04.1, 7.0.0-1011.11~24.04.1 +14
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 19 Jul 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 |
|---|---|---|
Ubuntu 26.04 LTSlinuxpkg:deb/ubuntu/linux?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSlinux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-gkepkg:deb/ubuntu/linux-gke?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A patch is available and should be applied by updating to the fixed Linux kernel versions. The fix involves enabling atomic updates for GCOV counters using the -fprofile-update=prefer-atomic compiler flag, which prevents concurrent access crashes. The patch is included in recent Linux kernel releases and distributions such as Ubuntu have issued security notices with updated kernel packages. Users should upgrade to the patched kernel versions as soon as possible to mitigate this vulnerability.
Description
A concurrency issue in the Linux kernel's GCOV instrumentation caused out-of-bounds memory writes during concurrent execution on multiple CPUs. This was due to non-atomic updates of global GCOV counters used in optimized loops, leading to inconsistent values and memory corruption. The flaw was fixed by enabling atomic counter updates via a compiler flag, preventing the compiler from merging counters with loop induction variables. This vulnerability has a critical severity with a CVSS score of 9.8 and affects multiple Linux kernel versions prior to 7.0.0-31.31 and several specific older versions. A patch is available and included in recent Linux kernel updates.
References
- nvd.nist.gov/vuln/detail/CVE-2026-63825 (opens in a new tab)
- git.kernel.org/stable/c/49d893b9cbcfc5802a32e53a64c6c6956670d65b (opens in a new tab)
- git.kernel.org/stable/c/56cb9b7d96b28a1173a510ab25354b6599ad3a33 (opens in a new tab)
- git.kernel.org/stable/c/5b959c1dbb4522b9e3ac4e26ad638b8784869841 (opens in a new tab)
- ubuntu.com/security/CVE-2026-63825 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-63825 (opens in a new tab)
- git.kernel.org/linus/56cb9b7d96b28a1173a510ab25354b6599ad3a33 (opens in a new tab)
- ubuntu.com/security/notices/USN-8726-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8727-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8728-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8760-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8781-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8726-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8726-3 (opens in a new tab)
- ubuntu.com/security/notices/USN-8800-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8760-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8728-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8726-4 (opens in a new tab)
- ubuntu.com/security/notices/USN-8728-3 (opens in a new tab)
- git.kernel.org/stable/c/4575852c23a10abc7648d31e4c12cf79d7391637 (opens in a new tab)
- git.kernel.org/stable/c/b0f7bd5eeb903a0021a80e9d704814e2a9d3998c (opens in a new tab)