CVE-2026-97557: Linux kernel · smb: client: avoid leaking refcount in cifs_queue_oplock_break()
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 7.5 High.
Data as of 26 Oct 2026, 12:55 UTC
- EPSS
- 0.6% chance of exploitation in 30 days – higher than 51% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 25 Sep 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
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 fix is available that modifies the reference counting logic in cifs_queue_oplock_break() to only increment the reference count after successful queueing of the work item. Users should apply the updated Linux kernel versions that include this fix. No additional mitigation is required beyond applying the official patch.
Description
A vulnerability in the Linux kernel's SMB client implementation (cifs_queue_oplock_break) causes a reference count leak when multiple oplock breaks occur while a work item is queued. This leak can lead to kernel bugs and failure of unmount operations on the CIFS filesystem. The issue arises because the reference count is incremented before queueing the work unconditionally, but if the work is not queued successfully, the reference is never decremented. The fix involves incrementing the reference count only after successful queueing of the work item.
References
- ubuntu.com/security/CVE-2026-97557 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-97557 (opens in a new tab)
- git.kernel.org/stable/c/dfe7b750c7e069873a8a57a11c816831a235618a (opens in a new tab)
- git.kernel.org/stable/c/9f2e63f1b2d5fc5b5423424902c091123e220e7e (opens in a new tab)
- git.kernel.org/stable/c/2ed2c29dd9593637cfa25ac1eb23241b20202778 (opens in a new tab)
- git.kernel.org/stable/c/af0193bbf1ac8c0f67f972998b0cc629d6116cf6 (opens in a new tab)
- nvd.nist.gov/vuln/detail/CVE-2026-97557 (opens in a new tab)
- git.kernel.org/stable/c/735a3a610136ae10f381d0909dff38e5b5c5f056 (opens in a new tab)
- git.kernel.org/stable/c/de2a6bcff2659bea40c7485115b57f0ae189fc01 (opens in a new tab)