--- title: "CVE-2025-39682: Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability" url: https://erroneo.us/security/cve/CVE-2025-39682/ description: "CVE-2025-39682 (Linux Kernel): Exploited in the wild (CISA KEV). In the Linux kernel, the following vulnerability has been resolved: tls: fix handling of…" type: vulnerability-record section: "Security Digest" date_published: 2025-09-05 date_modified: 2026-10-21 publisher: erroneo.us author: erroneo.us Security Desk cve: "CVE-2025-39682" kev: true cvss: 9.8 epss: 0.0288 license: All rights reserved. Quote with attribution and a link. --- # CVE-2025-39682: Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability **Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.) ## Should you act? - Yes, if you run Linux Kernel. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-09-18, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-09-21 ; treat that as the outer limit, not the target. - EPSS 2.9% , percentile 87: FIRST’s model estimates a 2.9% chance of exploitation activity in the next 30 days, higher than 87% of all scored CVEs (elevated). EPSS is a probability, not a verdict. - Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it. - Editorial verdict: Patch this week. Linux Kernel: Five Exploited Root Bugs Added to CISA KEV — Five local root bugs, all with fixes and most with public exploits, are now confirmed exploited; get every Linux host onto a current kernel and reboot this week, container hosts, CI runners and shared servers first. ## What it is In the Linux kernel, the following vulnerability has been resolved: tls: fix handling of zero-length records on the rxlist 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 rxlist. Next recvmsg() will pick it up from there. Queuing the skb to rxlist 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 rxlist, and it's zero length. ## Affected products (CVE record) - Linux Linux: 84c61fe1a75b4255df1e1e7c054c9e6d048da417 < 2902c3ebcca52ca845c03182000e8d71d3a5196f, 84c61fe1a75b4255df1e1e7c054c9e6d048da417 < c09dd3773b5950e9cfb6c9b9a5f6e36d06c62677, 84c61fe1a75b4255df1e1e7c054c9e6d048da417 < 3439c15ae91a517cf3c650ea15a8987699416ad9, 84c61fe1a75b4255df1e1e7c054c9e6d048da417 < 29c0ce3c8cdb6dc5d61139c937f34cb888a6f42e, 84c61fe1a75b4255df1e1e7c054c9e6d048da417 < 62708b9452f8eb77513115b17c4f8d1a22ebf843 - Linux Linux: 6.0 ## Severity - Linux CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H` ## Exploitation - CISA KEV: added 2026-09-18; federal due date 2026-09-21. Known ransomware use: Unknown. - CISA 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. - CISA SSVC assessment: exploitation active , automatable yes , technical impact total . - FIRST EPSS (model of 2026-10-21): 2.88% probability of exploitation activity in the next 30 days; percentile 87. ## Sources - [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/stable/c/2902c3ebcca52ca845c03182000e8d71d3a5196f) - [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/stable/c/c09dd3773b5950e9cfb6c9b9a5f6e36d06c62677) - [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/stable/c/3439c15ae91a517cf3c650ea15a8987699416ad9) - [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/stable/c/29c0ce3c8cdb6dc5d61139c937f34cb888a6f42e) - [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/stable/c/62708b9452f8eb77513115b17c4f8d1a22ebf843) - [CVE.org record CVE-2025-39682](https://www.cve.org/CVERecord?id=CVE-2025-39682) - [NVD entry CVE-2025-39682](https://nvd.nist.gov/vuln/detail/CVE-2025-39682) - [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-39682) - [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk) - [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk) - [lists.debian.org](https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html) - [cert-portal.siemens.com](https://cert-portal.siemens.com/productcert/html/ssa-032379.html) --- Source page: https://erroneo.us/security/cve/CVE-2025-39682/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt