CVE-2025-71070: Linux kernel · ublk: clean up user copy references on ublk server exit
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 7.8 High · fixed in 6.17.0-1018.18 : patch Linux kernel soon.
Data as of 26 Oct 2026, 14:05 UTC
- EPSS
- 0.1% chance of exploitation in 30 days – higher than 3% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 6.17.0-1018.18, 6.17.0-1013.13~24.04.1, 6.17.0-1012.12~24.04.1 +1
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 13 Jan 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 Linux kernel to 6.17.0-1018.18, 6.17.0-1013.13~24.04.1, 6.17.0-1012.12~24.04.1 or 6.17.0-22.22~24.04.1.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| linux-hwe-edge | Affected
| Fixed in
|
AI-suggested
A fix has been implemented in the Linux kernel to properly reset reference counts for all reference-counted ublk data copy modes when the ublk server exits. Users should apply the official kernel updates that include this fix. Since this is a kernel vulnerability, upgrading to a patched kernel version is the recommended remediation. Patch status is not explicitly confirmed here; check the vendor or kernel mailing list advisories for the exact fixed versions and update accordingly.
Description
In the Linux kernel, the following vulnerability has been resolved: ublk: clean up user copy references on ublk server exit If a ublk server process releases a ublk char device file, any requests dispatched to the ublk server but not yet completed will retain a ref value of UBLK_REFCOUNT_INIT. Before commit e63d2228ef83 ("ublk: simplify aborting ublk request"), __ublk_fail_req() would decrement the reference count before completing the failed request. However, that commit optimized __ublk_fail_req() to call __ublk_complete_rq() directly without decrementing the request reference count. The leaked reference count incorrectly allows user copy and zero copy operations on the completed ublk request. It also triggers the WARN_ON_ONCE(refcount_read(&io->ref)) warnings in ublk_queue_reinit() and ublk_deinit_queue(). Commit c5c5eb24ed61 ("ublk: avoid ublk_io_release() called after ublk char dev is closed") already fixed the issue for ublk devices using UBLK_F_SUPPORT_ZERO_COPY or UBLK_F_AUTO_BUF_REG. However, the reference count leak also affects UBLK_F_USER_COPY, the other reference-counted data copy mode. Fix the condition in ublk_check_and_reset_active_ref() to include all reference-counted data copy modes. This ensures that any ublk requests still owned by the ublk server when it exits have their reference counts reset to 0.
References
- nvd.nist.gov/vuln/detail/CVE-2025-71070 (opens in a new tab)
- git.kernel.org/stable/c/13456b4f1033d911f8bf3a0a1195656f293ba0f6 (opens in a new tab)
- git.kernel.org/stable/c/daa24603d9f0808929514ee62ced30052ca7221c (opens in a new tab)
- ubuntu.com/security/CVE-2025-71070 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2025-71070 (opens in a new tab)
- git.kernel.org/linus/daa24603d9f0808929514ee62ced30052ca7221c (opens in a new tab)
- ubuntu.com/security/notices/USN-8177-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8177-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8183-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8183-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8245-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8257-1 (opens in a new tab)