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.
do firstUpgrade to a fixed release: < 6.0, >= 6.1.149 and <= 6.1.*, >= 6.6.103 and <= 6.6.*, >= 6.12.44 and <= 6.12.* (+2 more below).
Can a WAF block it? No. The vulnerability is in the Linux kernel's TLS record handling, which is a network protocol but not HTTP. The malicious input is delivered via network packets at the TLS layer, not HTTP requests. Such low-level protocol attacks cannot be reliably detected or blocked by a web application firewall.
Also consider: patch
Based on an AI reading of the CVE description, and no vendor rule found yet. We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.
Is CVE-2025-39682 being exploited?
Yes. CVE-2025-39682 appears in CISA's Known Exploited Vulnerabilities catalog, which means exploitation in the wild has been confirmed and reported. Treat it as active rather than theoretical, and patch it ahead of higher-scoring vulnerabilities that carry no exploitation evidence.
How severe is CVE-2025-39682?
CVE-2025-39682 is rated Critical with a CVSS score of 9.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2025-39682?
Yes. A fix has been recorded for CVE-2025-39682. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2025-39682 affect?
CVE-2025-39682 affects linux:linux_kernel, debian:debian_linux, siemens:simatic_cn_4100_firmware. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
- affected>= 84c61fe1a75b4255df1e1e7c054c9e6d048da417 and < 2902c3ebcca52ca845c03182000e8d71d3a5196f
- affected>= 84c61fe1a75b4255df1e1e7c054c9e6d048da417 and < c09dd3773b5950e9cfb6c9b9a5f6e36d06c62677
- affected>= 84c61fe1a75b4255df1e1e7c054c9e6d048da417 and < 3439c15ae91a517cf3c650ea15a8987699416ad9
- affected>= 84c61fe1a75b4255df1e1e7c054c9e6d048da417 and < 29c0ce3c8cdb6dc5d61139c937f34cb888a6f42e
- affected>= 84c61fe1a75b4255df1e1e7c054c9e6d048da417 and < 62708b9452f8eb77513115b17c4f8d1a22ebf843
- affected6.0
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.
public exploits
Unvetted proof-of-concept code on GitHub: 2 GitHub proofs of concept
Listed so you can judge urgency, not as a recommendation to run anything. GitHub “proofs of concept” are unvetted: some are fake or carry malware. Exploit-DB marks the entries its staff verified.
cisa ssvc
- exploitation
- active
- automatable
- yes
- technical impact
- total
Assessed by CISA 19 Sept 2026 (SSVC 2.0.3).
timeline
- 5 Sept 2025Published
- 14 Oct 2025First proof-of-concept repository on GitHub (unvetted) · 38 days later
- 18 Sept 2026Added to CISA KEV (exploited in the wild) · 339 days (about 11 months) later
- 19 Sept 2026CISA SSVC assessment: exploitation active · 1 day later
- 21 Sept 2026CISA remediation due date (US federal agencies) · 2 days later
- 7 Oct 2026CVE record last updated · 17 days later
- 2 Nov 2026Analysed by vulneraibility.com · 26 days later
- Linkgit.kernel.org /stable/c/2902c3ebcca52ca845c03182000e8d71d3a5196f
- Linkgit.kernel.org /stable/c/c09dd3773b5950e9cfb6c9b9a5f6e36d06c62677
- Linkgit.kernel.org /stable/c/3439c15ae91a517cf3c650ea15a8987699416ad9
- Linkgit.kernel.org /stable/c/29c0ce3c8cdb6dc5d61139c937f34cb888a6f42e
- Linkgit.kernel.org /stable/c/62708b9452f8eb77513115b17c4f8d1a22ebf843
- Linklists.debian.org /debian-lts-announce/2025/10/msg00008.html
- Linkcert-portal.siemens.com /productcert/html/ssa-032379.html
- Linkcisa.gov /known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-39682
sources
- CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
- NVD: CVSS and CPE data
- CISA KEV catalog: exploitation, date added, due date
- CISA Vulnrichment (ADP): SSVC decision points
- FIRST EPSS: exploit probability and percentile
- PoC-in-GitHub: GitHub repositories that claim a proof of concept
- Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.