CVE-2025-39682

Published Sep 5, 2025

Last updated a day ago

Overview

AI description

Automated description summarized from trusted sources.

CVE-2025-39682 is a vulnerability found in the Linux kernel's Transport Layer Security (TLS) subsystem. The flaw specifically affects the handling of zero-length records within the `rx_list` during the `recvmsg()` process. This issue arises from a corner case where an initial zero-length record, pulled from the `rx_list`, disrupts assumptions made by the `recvmsg()` logic regarding zero-copy decryption and transitions between record types. This mishandling can lead to memory corruption and a use-after-free condition within the kernel's TLS receive path. A local, authenticated user can exploit this vulnerability by crafting a specific TLS traffic pattern that leaves a zero-length record queued on the `rx_list`, subsequently triggering the vulnerable code path during a `recvmsg()` call.

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.
Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD status: Undergoing Analysis
Products: linux_kernel, debian_linux

Risk scores

CVSS 3.1

Type: Primary
Base score: 7.1
Impact score: 5.2
Exploitability score: 1.8
Vector string: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
Severity: HIGH

Known exploits

Data from CISA

Vulnerability name: Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability
Exploit added on: Sep 18, 2026
Exploit action due: Sep 21, 2026
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.

Weaknesses

nvd@nist.gov: NVD-CWE-Other
134c704f-9b21-4f2e-91b3-4a467353bcc0: CWE-754

Hype score is a measure of social media activity compared against trending CVEs from the past 12 months. Max score 100.

Hype score: 19

Configurations

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References

Sources include official advisories and independent security research.