Vulnerability record · CVE-2025-39682 · published 5 September 2025
CVE-2025-39682: Linux kernel TLS zero-length record handling flaw on rx_list
Linux · Linux Kernel
The Linux kernel TLS receive path mishandles zero-length records that arrive from the rx_list, breaking the assumption that a record type change cannot occur after a zero-copy decrypt. This can leave the receive state inconsistent when processing subsequent recvmsg() calls. It matters because the flaw sits in core kernel TLS handling used by applications relying on kTLS.
Description
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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Automated analysis
high priorityCISA KEV listing indicates known exploitation, and the CVSS score is 7.1 HIGH, though the local attack vector and low EPSS temper urgency.
What it is
The Linux kernel TLS receive path mishandles zero-length records that arrive from the rx_list, breaking the assumption that a record type change cannot occur after a zero-copy decrypt. This can leave the receive state inconsistent when processing subsequent recvmsg() calls. It matters because the flaw sits in core kernel TLS handling used by applications relying on kTLS.
Impact
An attacker with local access can trigger the inconsistent receive path, leading to a high confidentiality impact and a high availability impact per the CVSS vector. The record does not state a concrete data-disclosure or crash outcome beyond those metrics.
Attack surface
Reached locally (AV:L) with low privileges (PR:L) and no user interaction (UI:N), per the CVSS vector, through the kernel TLS receive path. No remote or network vector is indicated in the record.
Exploitation
CVE-2025-39682 is listed in CISA KEV with a due date of 2026-09-21, indicating known exploitation, while EPSS is low at 0.00505 (41.99th percentile). References are patch and advisory links only, with no public exploit tag.
What to do
- Apply the upstream kernel patches referenced in the git.kernel.org stable commits.
- Update Debian systems per the Debian LTS advisory for this CVE.
- Track vendor guidance for affected Linux kernel and Debian packages, since the record does not list specific affected versions.
- Follow CISA BOD 26-04 patching guidance and evaluate asset exposure as directed in the KEV entry.
- If patching is not immediately possible, restrict local access to systems running kernel TLS workloads.
Detection
- Monitor kernel logs for TLS receive path errors or warnings around recvmsg handling.
- Audit which workloads use kernel TLS (kTLS) and correlate with unpatched kernel versions.
- Check asset inventories against the patched kernel versions from the referenced stable commits.
- Review local user activity on hosts running kTLS-enabled services for unusual recvmsg-driven behavior.
This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.
Exploitation in the wild
CISA added CVE-2025-39682 to the Known Exploited Vulnerabilities catalog on 18 September 2026 as "Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability". 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. Federal deadline 21 September 2026.
Affected products
3 vulnerable configurations from NVD's CPE data, grouped by vendor and product.
References
Track CVE-2025-39682 inside VULONE
Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.
Related vulnerabilities
Same products first, then exploited flaws of the same weakness class.
Source: NIST National Vulnerability Database (record CVE-2025-39682), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.
