CVE-2025-39964
crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg
Medium
Known exploited
Linux
- Severity
- 7.8 / 10
- Medium · CVSS 3.1
- Exploit chance (EPSS)
- 1.57%
- Chance of exploitation in the next 30 days. Higher than 75.38% of scored vulnerabilities.
- Known exploited
- Yes
- In CISA's catalog since Sep 18, 2026
- Weakness
- CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
- Fix
6.16.9- Upgrade Kernel to this version or later
Exploited in the wild. Linux Kernel Race Condition Vulnerability (Linux Kernel). 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. Due for U.S. federal agencies by Sep 21, 2026.
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.
Affected versions
Linux
| Package | Vulnerable | Fixed in |
|---|---|---|
| Kernel | >= 2.6.38, < 5.10.245>= 5.11.0, < 5.15.194>= 5.16.0, < 6.1.154>= 6.2.0, < 6.6.108>= 6.7.0, < 6.12.49>= 6.13.0, < 6.16.9 |
5.10.2455.15.1946.1.1546.6.1086.12.496.16.9 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
Kernel Linux → 6.16.9
Set Kernel to 6.16.9 or later in your manifest.
Severity breakdown
CVSS 3.1 7.8
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Attack vector
- Local
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Weakness
CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
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 to prevent it
- Architecture and Design: In languages that support it, use synchronization primitives. Only wrap these around critical code to minimize the impact on performance.
- Architecture and Design: Use thread-safe capabilities such as the data access abstraction in Spring.
- Architecture and Design: 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).
- Implementation: When using multithreading and operating on shared variables, only use thread-safe functions.
- Implementation: Use atomic operations on shared variables. Be wary of innocent-looking constructs such as "x++". This may appear atomic at the code layer, but it is actually non-atomic at the instruction layer, since it involves a read, followed by a computation, followed by a write.
- Implementation: Use a mutex if available, but be sure to avoid related weaknesses such as CWE-412.
- Implementation: Avoid double-checked locking (CWE-609) and other implementation errors that arise when trying to avoid the overhead of synchronization.
- Implementation: Disable interrupts or signals over critical parts of the code, but also make sure that the code does not go into a large or infinite loop.
- Implementation: Use the volatile type modifier for critical variables to avoid unexpected compiler optimization or reordering. This does not necessarily solve the synchronization problem, but it can help.
- Architecture and Design, Operation: Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.
References
Advisories
Packages
Other links
- cert-portal.siemens.com/productcert/html/ssa-019113.html
- cert-portal.siemens.com/productcert/html/ssa-457936.html
- 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
- cisa.gov/known-exploited-vulnerabilities-catalog
Timeline
- Published
- Added to CISA's Known Exploited Vulnerabilities catalog
- Remediation due for U.S. federal agencies
- Last updated by the source
- Latest EPSS score
Related advisories
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| CVE-2026-46300 net: skbuff: preserve shared-frag marker during coalescing | High Known exploited | Also affects Kernel |
| CVE-2026-31431 crypto: algif_aead - Revert to operating out-of-place | High Known exploited | Also affects Kernel |
| CVE-2025-39682 tls: fix handling of zero-length records on the rx_list | Critical Known exploited | Also affects Kernel |
| CVE-2025-38352 posix-cpu-timers: fix race between handle_posix_cpu_timers() and posix_cpu_timer_del() | High Known exploited | Also affects Kernel |
| CVE-2024-53197 ALSA: usb-audio: Fix potential out-of-bound accesses for Extigy and Mbox devices | High Known exploited | Also affects Kernel |
| CVE-2024-53150 ALSA: usb-audio: Fix out of bounds reads when finding clock sources | High Known exploited | Also affects Kernel |
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