Security readout for executives and security teams
Plain-English summary
A race condition in the Linux s390x ISM driver can corrupt commands sent to device firmware. Under certain workloads, an ISM function may enter an error state, break associated connections, and remain unavailable because the driver lacks automatic error recovery. The issue is important but applies specifically to systems using this architecture, device, and driver.
Executive priority
Treat remediation as urgent for production s390x systems relying on ISM-backed connections, particularly where device failure would interrupt critical services. Prioritize exposure confirmation first because applicability is narrow. The critical rating warrants attention, but the sources do not substantiate active attacks or confirmed confidentiality and integrity compromise.
Technical view
ism_cmd() failed to serialize request-response sequences even though firmware permits only one active sequence per ISM function. Concurrent CPUs could overwrite command inputs or mismatch commands and responses. Confirmed consequences include DMB tokens being treated as DMB IOVAs, invalid DMA, PCI PEC 2 events, and connection failures. The referenced stable commits add synchronization.
Likely exposure
Exposure is limited to Linux s390x hosts using an ISM function and an affected kernel revision. Other architectures and systems without the ISM driver are not identified as exposed. The supplied version data includes 4.19, 6.6.101, 6.12.41, 6.15.9, 6.16, and an ambiguous “0”; verify distribution backports and kernel provenance.
Exploitation context
The CVE is not listed in KEV, and the supplied sources provide no evidence of active exploitation or public weaponization. The documented trigger arose under certain concurrent workloads. Although the supplied CVSS vector specifies a network attack vector, the technical narrative does not establish how an unauthenticated remote attacker could reliably trigger the condition.
Researcher notes
Hard evidence covers command corruption, invalid DMA, device error states, and availability loss. Other outcomes are explicitly described as possible but not exhaustively established. The 9.8 CVSS vector assigns high confidentiality, integrity, and availability impact, yet the narrative provides no confirmed confidentiality or integrity compromise. No CWE is supplied.
Mitigation direction
- Identify s390x systems using the ISM driver and inventory their running kernel versions.
- Upgrade to a vendor-supported kernel containing the applicable referenced stable fix.
- If upgrading is delayed, seek vendor guidance; the sources name no separate workaround.
Validation and detection
- Confirm whether each host is s390x and has an ISM function bound to the ism driver.
- Compare kernel provenance against the applicable referenced stable commit or vendor advisory.
- Review kernel logs for zpci PEC 2 or PEC 3A events and ISM recovery-limitation messages.
- After remediation, monitor affected connection workloads for recurring ISM function errors or broken connections.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
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ATT&CK lookup starting points
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Credential and access behavior lookup
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Open ATT&CK lookupCVE-2025-39726 mapping review
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Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9LinuxVulnerability scoring details
Base CVSS 3.1 score
9.8CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
Source materials
- CVE List V5 sourceCVE List V5
- https://git.kernel.org/stable/c/faf44487dfc80817f178dc8de7a0b73f960d019bCVE reference, Linux
- https://git.kernel.org/stable/c/1194ad0d44d66b273a02a3a22882dc863a68d764CVE reference, Linux
- https://git.kernel.org/stable/c/fafaa4982bedb5532f5952000f714a3e63023f40CVE reference, Linux
- https://git.kernel.org/stable/c/897e8601b9cff1d054cdd53047f568b0e1995726CVE reference, Linux
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.