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CVE Record

CVE-2025-39931: crypto: af_alg - Set merge to zero early in af_alg_sendmsg

In the Linux kernel, the following vulnerability has been resolved: crypto: af_alg - Set merge to zero early in af_alg_sendmsg If an error causes af_alg_sendmsg to abort, ctx->merge may contain a garbage value from the previous loop. This may then trigger a crash on the next entry into af_alg_sendmsg when it attempts to do a merge that can't be done. Fix this by setting ctx->merge to zero near the start of the loop.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This Linux kernel issue can cause a crash in the kernel crypto AF_ALG message path after an earlier error leaves stale merge state behind. The public record does not provide CVSS, full impact scoring, or active exploitation evidence. Treat it as a kernel stability and availability risk pending vendor guidance.

Executive priority

Do not treat this as confirmed internet-exploited emergency from the supplied evidence. Prioritize normal kernel patch management, with faster handling for shared, multi-tenant, appliance, or operational technology systems where a kernel crash has high business impact.

Technical view

In af_alg_sendmsg, ctx->merge could retain a garbage value from a previous loop when an error aborts processing. On the next af_alg_sendmsg entry, the kernel may attempt an invalid merge and crash. The fix resets ctx->merge to zero near the start of the loop.

Likely exposure

Exposure is tied to Linux systems running affected kernel versions where the AF_ALG crypto interface is present and reachable by relevant local workloads. The bundle does not establish remote network exposure or list affected distributions beyond Linux kernel version data and Siemens advisories.

Exploitation context

The source bundle says CISA KEV is false and provides no cited evidence of active exploitation. It describes a crash condition, but not a weaponized exploit, exploit maturity, privileges required, or attack path.

Researcher notes

Key unknowns are exploit preconditions, required privileges, distribution backports, and whether the crash is reliably triggerable by untrusted users. The strongest evidence is the kernel fix description; validation should focus on kernel lineage and vendor advisory mapping.

Mitigation direction

  • Apply vendor-provided kernel updates containing the referenced stable commits.
  • Check Linux distribution advisories for packaged kernel fix availability.
  • Review Siemens advisories if Siemens products are in scope.
  • Prioritize systems where untrusted local workloads can access kernel crypto interfaces.

Validation and detection

  • Inventory Linux kernel versions across servers, appliances, and embedded systems.
  • Compare running kernels against vendor advisories and fixed package releases.
  • Confirm whether AF_ALG crypto support is enabled where risk matters.
  • Track Siemens advisory applicability for deployed Siemens products.
Prepared
Confidence
medium
Sources
11

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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CVE-2025-39931 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

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.

0CVSS vectors
3Timeline events
1ADP providers
10Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux8ff590903d5fc7f5a0a988c38267a3d08e6393a2, 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, 8ff590903d5fc7f5a0a988c38267a3d08e6393a2unaffected
LinuxLinux2.6.38, 0, 5.10.260, 5.15.211, 6.1.154, 6.6.108, 6.12.49, 6.16.9, 6.17affected
Weakness

CWE details

No CWE listed

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