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VulnerabilityPublished Updated

CVE-2025-39726: Linux kernel · s390/ism: fix concurrency management in ism_cmd()

Affects Linux kernelSource CVE Database V5

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Not known to be exploited · CVSS 9.8 Critical · fixed in fafaa4982bedb5532f5952000f714a3e63023f40 : patch Linux kernel as a priority.

Data as of 30 Oct 2026, 12:33 UTC

CVSS 3.1 base score
9.8Critical
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (Linux)CVSS 3.19.8
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers can reliably automate steps 1–4 of the kill chain
Technical impact
Total control over the software or total information disclosure

CISA SSVC assessment, 2026-10-15.

Patch
Available – fixed in fafaa4982bedb5532f5952000f714a3e63023f40, faf44487dfc80817f178dc8de7a0b73f960d019b, 79536c83cf38c285709757c4026da4ae151223ae +2
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 5 Sep 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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 30 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ 684b89bc39ce4f204b1a2b180f39f2eb36a6b695, < fafaa4982bedb5532f5952000f714a3e63023f40
Fixed in
  • fafaa4982bedb5532f5952000f714a3e63023f40
LinuxLinuxAffected
  • ≥ 684b89bc39ce4f204b1a2b180f39f2eb36a6b695, < faf44487dfc80817f178dc8de7a0b73f960d019b
Fixed in
  • faf44487dfc80817f178dc8de7a0b73f960d019b
LinuxLinuxAffected
  • ≥ 684b89bc39ce4f204b1a2b180f39f2eb36a6b695, < 79536c83cf38c285709757c4026da4ae151223ae
Fixed in
  • 79536c83cf38c285709757c4026da4ae151223ae
LinuxLinuxAffected
  • ≥ 684b89bc39ce4f204b1a2b180f39f2eb36a6b695, < 1194ad0d44d66b273a02a3a22882dc863a68d764
Fixed in
  • 1194ad0d44d66b273a02a3a22882dc863a68d764
LinuxLinuxAffected
  • ≥ 684b89bc39ce4f204b1a2b180f39f2eb36a6b695, < 897e8601b9cff1d054cdd53047f568b0e1995726
Fixed in
  • 897e8601b9cff1d054cdd53047f568b0e1995726
LinuxLinuxAffected
  • =4.19
Fixed in–

Description

In the Linux kernel, the following vulnerability has been resolved: s390/ism: fix concurrency management in ism_cmd() The s390x ISM device data sheet clearly states that only one request-response sequence is allowable per ISM function at any point in time. Unfortunately as of today the s390/ism driver in Linux does not honor that requirement. This patch aims to rectify that. This problem was discovered based on Aliaksei's bug report which states that for certain workloads the ISM functions end up entering error state (with PEC 2 as seen from the logs) after a while and as a consequence connections handled by the respective function break, and for future connection requests the ISM device is not considered -- given it is in a dysfunctional state. During further debugging PEC 3A was observed as well. A kernel message like [ 1211.244319] zpci: 061a:00:00.0: Event 0x2 reports an error for PCI function 0x61a is a reliable indicator of the stated function entering error state with PEC 2. Let me also point out that a kernel message like [ 1211.244325] zpci: 061a:00:00.0: The ism driver bound to the device does not support error recovery is a reliable indicator that the ISM function won't be auto-recovered because the ISM driver currently lacks support for it. On a technical level, without this synchronization, commands (inputs to the FW) may be partially or fully overwritten (corrupted) by another CPU trying to issue commands on the same function. There is hard evidence that this can lead to DMB token values being used as DMB IOVAs, leading to PEC 2 PCI events indicating invalid DMA. But this is only one of the failure modes imaginable. In theory even completely losing one command and executing another one twice and then trying to interpret the outputs as if the command we intended to execute was actually executed and not the other one is also possible. Frankly, I don't feel confident about providing an exhaustive list of possible consequences.

References

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