CVE-2025-39964
MediumExploitedPublic exploitLinux kernel: crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg
Published Oct 13, 2025 · Updated Oct 16, 2026 · Also known as DEBIAN-CVE-2025-39964, ROOT-OS-DEBIAN-11-CVE-2025-39964, ROOT-OS-DEBIAN-12-CVE-2025-39964, ROOT-OS-DEBIAN-13-CVE-2025-39964, ROOT-OS-UBUNTU-2204-CVE-2025-39964, ROOT-OS-UBUNTU-2404-CVE-2025-39964, UBUNTU-CVE-2025-39964, USN-7921-2, USN-7922-2, USN-7928-3, USN-7931-3, USN-7936-1
Key Facts
Patch immediately- CVE-2025-39964 is a medium-severity vulnerability (CVSS 5.5 v3.1) affecting linux-aws-6.12 (chainguard), linux-aws-6.18 (chainguard), linux-azure-6.12 (chainguard) and 22 more products.
- It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Sep 18, 2026. Public exploit code is available.
- EPSS estimates a 1.4% probability of exploitation in the next 30 days.
- Fixed versions are available, including bpftool 1:6.1.155-176.282.amzn2023, bpftool 4.18.0-553.168.1.el8_10, bpftool 5.10.245-1.ph4.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
5.5
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
EPSS (30-day exploit likelihood)
1.4%
Higher than 71.3% of all scored CVEs
Exploited in the wild
Yes
4 catalog listings
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2025-39964 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
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.
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CISA KEV | Sep 18, 2026 | Sep 21, 2026 | Not reported |
| Industry KEV feed | Sep 18, 2026 | Sep 21, 2026 | Not reported |
| CIRCL KEV | Sep 18, 2026 | Sep 21, 2026 | Not reported |
| ENISA EUVD | Sep 18, 2026 | n/a | Not reported |
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
4,849 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| linux-aws-6.12chainguard | See advisory | 6.12.76-r0 |
| linux-aws-6.18chainguard | See advisory | 6.18.17-r0 |
| linux-azure-6.12chainguard | See advisory | 6.12.76-r0 |
| linux-azure-6.18chainguard | See advisory | 6.18.17-r0 |
| linux-desktop-6.18chainguard | See advisory | 6.18.48-r0 |
Patched Releases
bpftool
1:6.1.155-176.282.amzn2023, 4.18.0-553.168.1.el8_10, 5.10.245-1.ph4, 5.15.0-313.189.5.2.el8uek, 5.15.0-313.189.5.2.el9uek, 5.15.0-314.193.5.3.el8uek, 5.15.0-314.193.5.3.el9uek, 5.15.0-315.196.5.1.el8uek, 5.15.0-315.196.5.1.el9uek, 6.1.155-1.ph5, 7.6.0+6.14.0-37.37
bpftool6.12
1:6.12.53-69.119.amzn2023
cluster-md-kmp-64kb
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
cluster-md-kmp-azure
6.12.0-160000.27.1, 6.12.0-160000.37.1
cluster-md-kmp-default
4.12.14-122.296.1, 4.12.14-122.328.1, 6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.135.1, 6.4.0-150600.23.92.1, 6.4.0-150700.53.34.1, 6.4.0-150700.53.81.1
cluster-md-kmp-rt
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150700.7.34.1, 6.4.0-150700.7.75.1
dlm-kmp-64kb
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dlm-kmp-azure
6.12.0-160000.27.1, 6.12.0-160000.37.1
dlm-kmp-default
4.12.14-122.296.1, 4.12.14-122.328.1, 6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.135.1, 6.4.0-150600.23.92.1, 6.4.0-150700.53.34.1, 6.4.0-150700.53.81.1
dlm-kmp-rt
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150700.7.34.1, 6.4.0-150700.7.75.1
dtb-allwinner
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-altera
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-amazon
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-amd
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-amlogic
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-apm
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-apple
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-arm
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-broadcom
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-cavium
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-exynos
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-freescale
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-hisilicon
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-lg
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
dtb-marvell
6.12.0-160000.27.1, 6.12.0-160000.37.1, 6.4.0-150600.23.92.1
Timeline
Publicly disclosed
Oct 13, 2025
Added to CISA KEV
Sep 18, 2026
Added to Industry KEV feed
Sep 18, 2026
Added to CIRCL KEV
Sep 18, 2026
Added to ENISA EUVD
Sep 18, 2026
Last updated
Oct 16, 2026
Weakness Type
- CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
- CWE-366 Race Condition within a Thread
References
- advisoryhttps://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39964.json
- advisoryhttps://git.kernel.org/linus/1b34cbbf4f011a121ef7b2d7d6e6920a036d5285
- advisoryhttps://nvd.nist.gov/vuln/detail/CVE-2025-39964
- advisoryhttps://security-tracker.debian.org/tracker/CVE-2025-39964
- advisoryhttps://ubuntu.com/security/CVE-2025-39964
FAQ
Common Questions.
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.
Affected: linux-aws-6.12 (chainguard); linux-aws-6.18 (chainguard); linux-azure-6.12 (chainguard), among others. The full list is in the CVE brief.
It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Sep 18, 2026.
Yes. It was added on Sep 18, 2026 with a federal remediation due date of Sep 21, 2026.
Public exploit code is available.
Fixed versions are available, including bpftool 1:6.1.155-176.282.amzn2023, bpftool 4.18.0-553.168.1.el8_10, bpftool 5.10.245-1.ph4.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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