CVE-2025-21886: Linux kernel · RDMA/mlx5: Fix implicit ODP hang on parent deregistration
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 5.5 Medium.
Data as of 29 Oct 2026, 23:42 UTC
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 27 Mar 2025
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 29 Oct 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 24.04 LTSlinux-raspi-realtimepkg:deb/ubuntu/linux-raspi-realtime?arch=source&distro=nobleOther threats | Affected
| Fixed in– |
Ubuntu 24.04 LTSlinux-realtimepkg:deb/ubuntu/linux-realtime?arch=source&distro=nobleOther threats | Affected
| Fixed in– |
Ubuntu 22.04 LTSlinux-allwinner-5.19pkg:deb/ubuntu/linux-allwinner-5.19?arch=source&distro=jammyOther threats | Affected
| Fixed in– |
Ubuntu 22.04 LTSlinux-aws-5.19pkg:deb/ubuntu/linux-aws-5.19?arch=source&distro=jammyOther threats | Affected
| Fixed in– |
Ubuntu 22.04 LTSlinux-aws-6.2pkg:deb/ubuntu/linux-aws-6.2?arch=source&distro=jammyOther threats | Affected
| Fixed in– |
Ubuntu 22.04 LTSlinux-aws-6.5pkg:deb/ubuntu/linux-aws-6.5?arch=source&distro=jammyOther 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 corrects the reference count management in the affected function. Users should apply the updated Linux kernel versions that include this patch to prevent the hang. No additional mitigation steps are indicated.
Description
CVE-2025-21886 addresses a vulnerability in the Linux kernel's RDMA/mlx5 driver where improper reference count management during parent deregistration could cause a hang. The flaw involves the destroy_unused_implicit_child_mr() function, which increments a reference count without a guaranteed corresponding decrement, leading to potential blocking of tasks. This issue has been fixed by correcting the reference count handling to prevent the hang.
References
- ubuntu.com/security/CVE-2025-21886 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2025-21886 (opens in a new tab)
- git.kernel.org/linus/3d8c6f26893d55fab218ad086719de1fc9bb86ba (opens in a new tab)
- git.kernel.org/stable/c/3d8c6f26893d55fab218ad086719de1fc9bb86ba (opens in a new tab)
- git.kernel.org/stable/c/a095ede2daca49d15e74d66d014883f2fa8bb924 (opens in a new tab)
- git.kernel.org/stable/c/cb96ae783e7249e8e5a50c22952c0bb2983133df (opens in a new tab)