CVEs / CVE-2025-39682
CVE-2025-39682: Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability
- Known exploited in the CISA KEV catalog since 18 Sep 2026
- critical 9.8 CVSS 3.1 (NVD)
- EPSS 3.25% chance of exploitation in the next 30 days, higher than 88% of CVEs (30 Oct 2026)
- Last changed at its sources
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Summary
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.
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.
Affected and fixed versions
| Product | Affected | Fixed in |
|---|---|---|
| Linux Linux | from 84c61fe1a75b4255df1e1e7c054c9e6d048da417, before 2902c3ebcca52ca845c03182000e8d71d3a5196f | 2902c3ebcca52ca845c03182000e8d71d3a5196f |
| Linux Linux | from 84c61fe1a75b4255df1e1e7c054c9e6d048da417, before c09dd3773b5950e9cfb6c9b9a5f6e36d06c62677 | c09dd3773b5950e9cfb6c9b9a5f6e36d06c62677 |
| Linux Linux | from 84c61fe1a75b4255df1e1e7c054c9e6d048da417, before 3439c15ae91a517cf3c650ea15a8987699416ad9 | 3439c15ae91a517cf3c650ea15a8987699416ad9 |
| Linux Linux | from 84c61fe1a75b4255df1e1e7c054c9e6d048da417, before 29c0ce3c8cdb6dc5d61139c937f34cb888a6f42e | 29c0ce3c8cdb6dc5d61139c937f34cb888a6f42e |
| Linux Linux | from 84c61fe1a75b4255df1e1e7c054c9e6d048da417, before 62708b9452f8eb77513115b17c4f8d1a22ebf843 | 62708b9452f8eb77513115b17c4f8d1a22ebf843 |
| Linux Linux | 6.0 | — |
| Siemens SIMATIC CN 4100 | before V5.0 | V5.0 |
| Product | Affected | Fixed in |
|---|---|---|
| Kernel (Linux) | from 6.0.0, before 6.1.149 | 6.1.149 |
| Kernel (Linux) | from 6.2.0, before 6.6.103 | 6.6.103 |
| Kernel (Linux) | from 6.7.0, before 6.12.44 | 6.12.44 |
| Kernel (Linux) | from 6.13.0, before 6.16.4 | 6.16.4 |
Exploitation
| In CISA KEV since | 18 Sep 2026 |
|---|---|
| Due date for US federal agencies | 21 Sep 2026 |
| Used in ransomware campaigns | Unknown |
| 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. |
Severity
| CVSS 3.1 | 9.8 criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HScored by NVD |
|---|---|
| Weakness | CWE-754 |
References
- CVE-2025-39682 on NVD
- CVE-2025-39682 in the CISA KEV catalog
- https://git.kernel.org/stable/c/2902c3ebcca52ca845c03182000e8d71d3a5196f (cited by CISA)
- https://git.kernel.org/stable/c/c09dd3773b5950e9cfb6c9b9a5f6e36d06c62677 (cited by CISA)
- https://git.kernel.org/stable/c/3439c15ae91a517cf3c650ea15a8987699416ad9 (cited by CISA)
- https://git.kernel.org/stable/c/29c0ce3c8cdb6dc5d61139c937f34cb888a6f42e (cited by CISA)
- https://git.kernel.org/stable/c/62708b9452f8eb77513115b17c4f8d1a22ebf843 (cited by CISA)
- https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk (cited by CISA)
- https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk (cited by CISA)
- CVE-2025-39682 on OSV
- https://git.kernel.org/stable/c/2902c3ebcca52ca845c03182000e8d71d3a5196f Patch
- https://git.kernel.org/stable/c/29c0ce3c8cdb6dc5d61139c937f34cb888a6f42e Patch
- https://git.kernel.org/stable/c/3439c15ae91a517cf3c650ea15a8987699416ad9 Patch
- https://git.kernel.org/stable/c/62708b9452f8eb77513115b17c4f8d1a22ebf843 Patch
- https://git.kernel.org/stable/c/c09dd3773b5950e9cfb6c9b9a5f6e36d06c62677 Patch
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html Mailing List, Third Party Advisory
- https://cert-portal.siemens.com/productcert/html/ssa-032379.html Third Party Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-39682 US Government Resource
Sources
Exploitation status from the CISA Known Exploited Vulnerabilities catalog. EPSS scores from FIRST. Descriptions, severity and references from the National Vulnerability Database. Open-source package versions from OSV (CC-BY 4.0). Text is shown as each source states it; Stackurity does not edit it. Check the vendor's advisory before acting.
This product uses data from the NVD API but is not endorsed or certified by the NVD.