Linux · Kernel
CVE-2025-39682
tls: fix handling of zero-length records on the rx_list
What it is
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.
CISA: Linux Kernel contains an improper check for unusual or exceptional conditions vulnerability in the TLS receive path which allows a zero-length record retrieved from the rx_list to bypass the intended recvmsg() record-type handling, potentially causing subsequent TLS records to be processed using incorrect zero-copy and queuing assumptions. The impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.
What to do
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.
Deadline for US federal agencies: September 21, 2026
- Added to the CISA list
- September 18, 2026
- Published
- September 5, 2025
- Severity
- Critical 9.8 CVSS 3.1
- Chance of attacks in the next 30 days (EPSS)
- 3.3% in the top 11.7% of all known vulnerabilities
- Weakness
- CWE-754
- More details
- NVD · CVE.org · CISA
All references (5)
- https://git.kernel.org/stable/c/2902c3ebcca52ca845c03182000e8d71d3a5196f
- https://git.kernel.org/stable/c/c09dd3773b5950e9cfb6c9b9a5f6e36d06c62677
- https://git.kernel.org/stable/c/3439c15ae91a517cf3c650ea15a8987699416ad9
- https://git.kernel.org/stable/c/29c0ce3c8cdb6dc5d61139c937f34cb888a6f42e
- https://git.kernel.org/stable/c/62708b9452f8eb77513115b17c4f8d1a22ebf843
More exploited flaws from Linux
| Added | Vulnerability | Product | Severity | Attack chance |
|---|---|---|---|---|
| Sep 18, 2026 | Race Condition | Kernel | High 7.8 | 1.6% |
| Sep 18, 2026 | Out-of-Bounds Write | Kernel | High 8.8 | 0.9% |
| Aug 27, 2026 | Unspecified | Kernel | High 7.8 | 0.7% |
| Aug 26, 2026 | Out-of-Bounds Write | Kernel | High 7.8 | 8.9% |
| Jun 2, 2026 | Improper Authentication | Kernel | High 7.8 | 5.5% |
| May 1, 2026 | Incorrect Resource Transfer Between Spheres | Kernel | High 7.8 | 98% |
| Jan 26, 2026 | Integer Overflow | Kernel | High 7.8 | 15% |
| Oct 6, 2025 | Heap Out-of-Bounds Write | Kernel | High 8.3 | 79% |
Sources: Known Exploited Vulnerabilities (CISA, public domain), CVE records (cve.org) and EPSS (FIRST). The chance of attacks is the EPSS estimate that someone will try to exploit the flaw in the next 30 days.