CVE-2025-39964 — Linux Kernel Race Condition Vulnerability
In the Linux kernel, the following vulnerability has been resolved: crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg Issuing two writes to the same af_alg socket is bogus as the data will be interleaved in an unpredictable fashion. Furthermore, concurrent writes may create inconsistencies in the internal socket state. Disallow this by adding a new ctx->write field that indiciates exclusive ownership for writing.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- Confirmed exploitation (CISA KEV)+35
- Public exploit/PoC (github)+6
- EPSS 1.3% (30-day exploitation probability)+11
- Technical severity (medium)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
CISA required action CISA
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
US federal deadline: Sep 21, 2026 — passed 25 day(s) ago
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Linux Linux, Linux Linux Kernel, Siemens Simatic S7-1500 Cpu 1518-4 Pn/dp Mfp Firmware…).
- Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
- Apply the fixed version or the patch documented under Remediation.
- Search available logs for exploit probes matching the vulnerability class (logic error), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Linux | Linux | version 2.6.38≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 and < 1b34cbbf4f011a121ef7b2d7d6e6920a036d5285≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 and < 45bcf60fe49b37daab1acee57b27211ad1574042≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 and < 9aee87da5572b3a14075f501752e209801160d3d≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 and < 7c4491b5644e3a3708f3dbd7591be0a570135b84≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 and < 1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 and < e4c1ec11132ec466f7362a95f36a506ce4dc08c9≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 and < 0f28c4adbc4a97437874c9b669fd7958a8c6d6ce | Vulnerable | CVE Program (cve.org) e CISA ADP |
| Linux | Linux Kernel |
version 6.17-rc6≥ 2.6.38 and < 5.10.245version 6.17-rc5version 6.17-rc4version 6.17-rc3version 6.17-rc2version 6.17-rc1≥ 6.13 and < 6.16.9 and 4 more≥ 6.7 and < 6.12.49≥ 6.2 and < 6.6.108≥ 5.16 and < 6.1.154≥ 5.11 and < 5.15.194 |
Vulnerable | NIST National Vulnerability Database |
| Siemens | Simatic S7-1500 Cpu 1518-4 Pn/dp Mfp Firmware | ≥ 3.1.6 | Vulnerable | NIST National Vulnerability Database |
| Siemens | Simatic S7-1500 Cpu 1518f-4 Pn/dp Mfp Firmware | ≥ 3.1.6 | Vulnerable | NIST National Vulnerability Database |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 7.8 | CVSS 3.1 | High | 1.8 | 5.9 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database |
| 7.8 | CVSS 3.1 | High | — | — | Linux via CVE Program (cve.org) e CISA ADP |
| 5.5 | CVSS 3.1 | Medium | 1.8 | 3.6 | nvd@nist.gov via NIST National Vulnerability Database |
| 3.3 | CVSS 3.1 | Low | — | — | GitHub, Inc. via GitHub Security Advisories |
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
CISA KEV details CISA
CISA lists a CVE once it has evidence of exploitation against real targets.
CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a reference date.
Public exploits, PoCs and detection templates
Public code that demonstrates or tests the flaw raises the odds of mass exploitation — and Nuclei templates help find vulnerable assets in your environment.
- CVE-2025-39964 EXP ★ 3 Nov 13, 2025
- Tracking CVE-2025-39964, the Linux kernel AF_ALG concurrent-write race ★ 0 Sep 20, 2026
Warning: public PoCs are sometimes disguised malware. Use them only for authorized testing in an isolated environment. This portal does not host exploit code — it only points to the sources.
EPSS over time FIRST
Oct 12, 2026 → Oct 15, 2026 · 4 reading(s) · max 1.31%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
- Hunt retroactively in logs from before Sep 18, 2026 (KEV listing): exploitation may have started earlier.
Timeline
What happened to this CVE, newest first.
- 2026
- Source status changed · Modified → Analyzed
- Source status changed · Analyzed → Modified
- Affected products added · linux/linux
- SSVC assessment updated
- Record published
- Fix documented
- Affected products added · linux/linux kernel, siemens/simatic s7-1500 cpu 1518-4 pn/dp mfp firmware, siemens/simatic s7-1500 cpu 1518f-4 pn/dp mfp
- CVSS changed · 5.5
- Source status changed · → Analyzed
- Added to CISA KEV (detected)
- Record created in this database
- Added to CISA KEV catalog
- 2025
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 3× References added · Oct 13, 2026 – Oct 15, 2026
- 1× Official description updated · Oct 13, 2026 – Oct 13, 2026
References
12 on the record
- git.kernel.org/stable/c/45bcf60fe49b37daab1acee57b27211ad1574042
- git.kernel.org/stable/c/7c4491b5644e3a3708f3dbd7591be0a570135b84
- git.kernel.org/stable/c/1b34cbbf4f011a121ef7b2d7d6e6920a036d5285
- git.kernel.org/stable/c/0f28c4adbc4a97437874c9b669fd7958a8c6d6ce
- git.kernel.org/stable/c/1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8
- git.kernel.org/stable/c/9aee87da5572b3a14075f501752e209801160d3d
- git.kernel.org/stable/c/e4c1ec11132ec466f7362a95f36a506ce4dc08c9
- www.cisa.gov/known-exploited-vulnerabilities-catalog
- nvd.nist.gov/vuln/detail/CVE-2025-39964
- github.com/advisories/GHSA-wr5g-mfhw-rpfj
- cert-portal.siemens.com/productcert/html/ssa-457936.html
- cert-portal.siemens.com/productcert/html/ssa-019113.html
Elsewhere on this site
Related CVEs (same products)
- Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 15h
- Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 15h
- Unknown CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
- Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
- Unknown CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
- Unknown CVE-2026-98427 net/sched: codel: bound the dropping loop per dequeue call 1d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2025-39964 is "Linux Kernel Race Condition Vulnerability", rated Medium. It affects Linux (Linux); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 5.5 describes technical severity. EPSS 1.31% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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