CVE-2025-39682: Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability

CISA Known Exploited Vulnerabilities

Name

Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability

Vendor

Linux

Product

Kernel

Added to the catalog

2026-09-18

Due date for US federal agencies

2026-09-21

Weaknesses

CWE-754

Catalog version

2026.10.30

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.

Required action (CISA)

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.

Ransomware use: CISA does not mark known use of this vulnerability in ransomware campaigns.

Links in CISA's notes

• 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
• https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
• https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
• https://nvd.nist.gov/vuln/detail/CVE-2025-39682

Read on 2026-11-02T23:39:54.475Z under licence cisa-kev-cc0@b0067899 from https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json

NVD analysis

Status

Analyzed

Published

2025-09-05T18:15:44.670

Last modified

2026-10-19T21:10:00.160

Weaknesses

NVD-CWE-Other, CWE-754

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.

References

• 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)

This product uses the NVD API but is not endorsed or certified by the NVD.

Read on 2026-11-02T23:42:22.836Z under licence nvd-api-terms-of-use@ff2a5288 from https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2025-39682

CVE record

Title (CNA)

tls: fix handling of zero-length records on the rx_list

Assigner

Linux

State

PUBLISHED

Published

2025-09-05T17:20:48.657Z

Updated

2026-10-07T17:56:14.826Z

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.

References

• 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

Read on 2026-11-03T02:16:25.507Z under licence cve-terms-of-use@81bfa2f3 from https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2025/39xxx/CVE-2025-39682.json

Defensive techniques (MITRE D3FEND)

D3FEND maps these defensive techniques to the weakness (CWE) that NVD lists for this CVE, through the digital artifacts the weakness affects. D3FEND does not say they stop this vulnerability.

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