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Public proof of conceptFix available

CVE-2025-39946

A public proof of concept exists; no exploitation attested.

  • Published2025-10-04
  • Fixed in6.16.9 · 6.12.49 · 6.6.108 · 6.1.154

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

In the Linux kernel, the following vulnerability has been resolved: tls: make sure to abort the stream if headers are bogus Normally we wait for the socket to buffer up the whole record before we service it. If the socket has a tiny buffer, however, we read out the data sooner, to prevent connection stalls. Make sure that we abort the connection when we find out late that the record is actually invalid. Retrying the parsing is fine in itself but since we copy some more data each time before we parse we can overflow the allocated skb space. Constructing a scenario in which we're under pressure without enough data in the socket to parse the length upfront is quite hard. syzbot figured out a way to do this by serving us the header in small OOB sends, and then filling in the recvbuf with a large normal send. Make sure that tls_rx_msg_size() aborts strp, if we reach an invalid record there's really no way to recover.

Timeline

dates in UTC
  1. 2025-10-0408:15CVE publishedNVD
  2. 2026-10-2319:23First public proof of conceptPoC-in-GitHub

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2025-39946?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2025-39946?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Linux linux kernel
BranchAffectedFixed in
6.x≥ 6.13, < 6.16.96.16.9
6.x≥ 6.7, < 6.12.496.12.49
6.x≥ 6.2, < 6.6.1086.6.108
6.x≥ 6.0, < 6.1.1546.1.154
6.17= 6.17no fix published

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

  1. Update Linux linux kernel to 6.16.9 · 6.12.49 · 6.6.108 · 6.1.154

Advisories and patches

Detection

read 2026-10-23 19:24 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
1 repository, unverifiedfarazsth98/exploit-CVE-2025-39946
PoC-in-GitHub

Sources

Technical details

CVSS v3 Vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Published
2025-10-04
Last Modified
2026-10-19
NVD status
Analyzed

Frequently asked questions

What is CVE-2025-39946?

In the Linux kernel, the following vulnerability has been resolved: tls: make sure to abort the stream if headers are bogus Normally we wait for the socket to buffer up the whole record before we service it. If the socket has a tiny buffer, however, we read out the data sooner, to prevent connection stalls. Make sure that we abort the connection when we find out late that the record is actually invalid. Retrying the parsing is fine in itself but since we copy some more data each time before we parse we can overflow the allocated skb space. Constructing a scenario in which we're under pressure without enough data in the socket to parse the length upfront is quite hard. syzbot figured out a way to do this by serving us the header in small OOB sends, and then filling in the recvbuf with a large normal send. Make sure that tls_rx_msg_size() aborts strp, if we reach an invalid record there's really no way to recover.

Is CVE-2025-39946 actively exploited?

Active exploitation of CVE-2025-39946 has not been confirmed. Its EPSS score was 9.6% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2025-39946?

CVE-2025-39946 has a CVSS v3 base score of 5.5 (MEDIUM severity), with vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

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