What is CVE-2025-39682?
In the Linux kernel, the following vulnerability has been resolved: tls: fix handling of zero-length records on the rx_list Each recvmsg() call must process either - only contiguous DATA records (any number of them) - one non-DATA record If the next record has different type than what has already been processed we break out of the main processing loop. If the record has already been decrypted (which may be the case for TLS 1.3 where we don't know type until decryption) we queue the pending record to the rx_list. Next recvmsg() will pick it up from there. Queuing the skb to rx_list after zero-copy decrypt is not possible, since in that case we decrypted directly to the user space buffer, and we don't have an skb to queue (darg.skb points to the ciphertext skb for access to metadata like length). Only data records are allowed zero-copy, and we break the processing loop after each non-data record. So we should never zero-copy and then find out that the record type has changed. The corner case we missed is when the initial record comes from rx_list, and it's zero length.
Timeline
- 2025-09-05Published to the U.S. National Vulnerability Database (NVD)
- 2026-09-18Added to the CISA Known Exploited Vulnerabilities (KEV) catalog
- 2026-09-21CISA federal remediation deadline (BOD 22-01)
- 2026-10-19NVD record last updated
CISA Known Exploited Vulnerability
Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability
Affected product
Linux Kernel
NVD also lists CPE entries for: Linux Kernel, Siemens Simatic Cn 4100 Firmware, Siemens Simatic Cn 4100, Debian Linux
Remediation Steps
- Apply the latest Linux kernel security patches
- Prioritize patching systems exposed to untrusted networks
- Review system logs for signs of active exploitation
- Test patches in non-production environments before deployment
References
- https://git.kernel.org/stable/c/2902c3ebcca52ca845c03182000e8d71d3a5196f
- https://git.kernel.org/stable/c/29c0ce3c8cdb6dc5d61139c937f34cb888a6f42e
- https://git.kernel.org/stable/c/3439c15ae91a517cf3c650ea15a8987699416ad9
- https://nvd.nist.gov/vuln/detail/CVE-2025-39682
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog
Referenced in our briefings & reports
- Vulnerability Priority Report – Week 2 of October 2026 (October 12 – 18)
- Vulnerability Priority Report – Week 1 of October 2026 (October 5 – 11)
- Vulnerability Priority Report – Week 4 of September 2026 (September 28 – October 4)
- Vulnerability Priority Report – Week 3 of September 2026 (September 21 – 27)
Related vulnerabilities
- CVE-2026-53362 – Linux Kernel (same product)
- CVE-2026-53266 – Linux Kernel (same product)
- CVE-2026-46300 – Linux Kernel (same product)
- CVE-2025-39964 – Linux Kernel (same product)
- CVE-2026-102489 – Zammad GmbH Zammad (same product)
- CVE-2026-102490 – Zammad GmbH Zammad (same product)
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