Linux Kernel Race Condition
CVE-2025-39964 is a medium-severity concurrent execution using shared resource with improper synchronization vulnerability in Linux, with a CVSS 3.1 base score of 5.5 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 0f28c4adbc4a97437874c9b669fd7958a8c6d6ce, e4c1ec11132ec466f7362a95f36a506ce4dc08c9, 1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on September 18, 2026, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update Linux to 0f28c4adbc4a97437874c9b669fd7958a8c6d6ce or e4c1ec11132ec466f7362a95f36a506ce4dc08c9 or 1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8 or 7c4491b5644e3a3708f3dbd7591be0a570135b84, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.10.245 or 5.15.194 or 6.1.154 or 6.6.108, whichever matches your release line, or a later version.
- CISA's required action: 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.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 up to, but not including, 0f28c4adbc4a97437874c9b669fd7958a8c6d6ce; 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 up to, but not including, e4c1ec11132ec466f7362a95f36a506ce4dc08c9; 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 up to, but not including, 1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8; 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 up to, but not including, 7c4491b5644e3a3708f3dbd7591be0a570135b84; 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 up to, but not including, 9aee87da5572b3a14075f501752e209801160d3d; 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 up to, but not including, 45bcf60fe49b37daab1acee57b27211ad1574042; 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 up to, but not including, 1b34cbbf4f011a121ef7b2d7d6e6920a036d5285; 2.6.38 | 0f28c4adbc4a97437874c9b669fd7958a8c6d6ce, e4c1ec11132ec466f7362a95f36a506ce4dc08c9, 1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8, 7c4491b5644e3a3708f3dbd7591be0a570135b84, 9aee87da5572b3a14075f501752e209801160d3d, 45bcf60fe49b37daab1acee57b27211ad1574042 |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Linux | Linux Kernel | 2.6.38 up to, but not including, 5.10.245; 5.11 up to, but not including, 5.15.194; 5.16 up to, but not including, 6.1.154; 6.2 up to, but not including, 6.6.108; 6.7 up to, but not including, 6.12.49; 6.13 up to, but not including, 6.16.9; 6.17 | 5.10.245, 5.15.194, 6.1.154, 6.6.108, 6.12.49, 6.16.9 |
| Siemens | Simatic S7-1500 Cpu 1518-4 Pn/dp Mfp Firmware | 3.1.6 and later | Not stated |
| Siemens | Simatic S7-1500 Cpu 1518f-4 Pn/dp Mfp Firmware | 3.1.6 and later | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA |
| CVSS 3.1 | 5.5 | Medium | NVD |
Official description
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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Concurrent Execution using Shared Resource with Improper Synchronization
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
How developers prevent this class of flaw
- In languages that support it, use synchronization primitives. Only wrap these around critical code to minimize the impact on performance.
- Use thread-safe capabilities such as the data access abstraction in Spring.
- Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring. Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: active, automatable: no, technical impact: total).
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/0f28c4adbc4a97437874c9b669fd7958a8c6d6ce
- git.kernel.org/stable/c/1b34cbbf4f011a121ef7b2d7d6e6920a036d5285
- git.kernel.org/stable/c/1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8
- git.kernel.org/stable/c/45bcf60fe49b37daab1acee57b27211ad1574042
- git.kernel.org/stable/c/7c4491b5644e3a3708f3dbd7591be0a570135b84
- git.kernel.org/stable/c/9aee87da5572b3a14075f501752e209801160d3d
- git.kernel.org/stable/c/e4c1ec11132ec466f7362a95f36a506ce4dc08c9
Third-party and government advisories
- cert-portal.siemens.com/productcert/html/ssa-019113.htmlThird Party Advisory
- cert-portal.siemens.com/productcert/html/ssa-457936.htmlThird Party Advisory
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-39964US Government Resource
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