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

Q: How do I fix CVE-2025-39682?

linux kernel: upgrade to 6.1.149, 6.6.103, 6.12.44, 6.16.4; debian linux: mitigate or apply the listed mitigation; simatic cn 4100 firmware: upgrade to 5.0. Exact commands for each OS are on this page.

Q: Is CVE-2025-39682 being exploited?

Yes. CVE-2025-39682 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

Q: What does CVE-2025-39682 affect?

CVE-2025-39682 affects linux kernel, debian linux, simatic cn 4100 firmware. Severity is critical (CVSS 9.8). 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 recor

Q: How urgent is CVE-2025-39682?

Priority 99/100. Critical severity; Exploited in the wild (CISA KEV); Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist

Patch now

CRITICAL 9.8EXPLOITEDREMOTEWATCHLISTUPGRADEMITIGATEUPGRADE

CVE-2025-39682 is a critical-severity flaw (CVSS 9.8) affecting linux kernel, debian linux, simatic cn 4100 firmware, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

Critical severity
Exploited in the wild (CISA KEV)
Public exploit reference
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.9% (top 13%)
CISA exploited list	Yes, fix due 2026-09-21
Weakness	CWE-754
Published	2025-09-05
Last modified	2026-10-19

Publisher (CNA): kernel.org · Vendor: debian · linux · siemens

Last updated 2026-10-19 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-09-05 18:15 UTCPublished CVE record published
2026-09-18Exploited Added to the CISA Known Exploited Vulnerabilities list
2026-09-21Deadline CISA due date for US federal agencies to patch
2026-10-19 21:10 UTCUpdated Record last modified

linux linux kernel UPGRADE

Affected: >= 6.0 and < 6.1.149 · >= 6.2 and < 6.6.103 · >= 6.7 and < 6.12.44 · >= 6.13 and < 6.16.4 · 6.17 rc1 · 6.17 rc2

Fixed in: 6.1.149, 6.6.103, 6.12.44, 6.16.4

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

debian debian linux MITIGATE

Affected: 11.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 11.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

siemens simatic cn 4100 firmware UPGRADE

Affected: < 5.0

Fixed in: 5.0

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora 46 · uv · FIXED · 0.13.5-1.fc46 · FEDORA-2026-61ea5a28c6 · source

sudo dnf upgrade --advisory=FEDORA-2026-61ea5a28c6

Debian 12 · linux · FIXED · 6.1.153-1

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.1.153-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · linux · FIXED · 6.12.48-1

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.12.48-1" && echo PATCHED || echo STILL-VULNERABLE

RHEL 10 · kernel · FIXED · kernel-6.12.0-55.37.1.el10_0

sudo dnf upgrade --advisory=RHSA-2025:16904 rpm -q kernel

RHEL 9 · kernel · FIXED · kernel-5.14.0-570.49.1.el9_6

sudo dnf upgrade --advisory=RHSA-2025:16880 rpm -q kernel

RHEL 9.2 Update Services for SAP Solutions · kernel · FIXED · kernel-5.14.0-284.144.1.el9_2

sudo dnf upgrade --advisory=RHSA-2025:19224 rpm -q kernel

RHEL 9.2 Update Services for SAP Solutions · kernel-rt · FIXED · kernel-rt-5.14.0-284.144.1.rt14.429.el9_2

sudo dnf upgrade --advisory=RHSA-2025:19223 rpm -q kernel-rt

RHEL 9.4 Extended Update Support · kernel · FIXED · kernel-5.14.0-427.96.1.el9_4

sudo dnf upgrade --advisory=RHSA-2025:19104 rpm -q kernel

Amazon Linux 2023 · see advisory · FIXED · ALAS2023-2025-1208 · source

sudo dnf update --advisory=ALAS2023-2025-1208

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

GitHub PoC: khoatran107/cve-2025-39682 (6 stars)
GitHub PoC: suominen/CVE-2025-39682 (0 stars)

Verify at the official source NVD · CVE Program · CISA KEV catalog · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-39682?

linux kernel: upgrade to 6.1.149, 6.6.103, 6.12.44, 6.16.4; debian linux: mitigate or apply the listed mitigation; simatic cn 4100 firmware: upgrade to 5.0. Exact commands for each OS are on this page.

Is CVE-2025-39682 being exploited?

Yes. CVE-2025-39682 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2025-39682 affect?

CVE-2025-39682 affects linux kernel, debian linux, simatic cn 4100 firmware. Severity is critical (CVSS 9.8). 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 recor

How urgent is CVE-2025-39682?

Priority 99/100. Critical severity; Exploited in the wild (CISA KEV); Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Linux kernel vulnerabilities · Debian vulnerabilities

Related CVEs

CVE-2026-64439 CRITICAL 9.8 UPGRADE In the Linux kernel, the following vulnerability has been resolved: crypto: krb5 - filter out async aead impl
CVE-2026-64312 HIGH 7.5 UPGRADE In the Linux kernel, the following vulnerability has been resolved: crypto: pcrypt - restore callback for non
CVE-2026-64313 HIGH 8.8 UPGRADE In the Linux kernel, the following vulnerability has been resolved: crypto: ecc - Fix carry overflow in vli m
CVE-2026-64438 HIGH 8.8 UPGRADE In the Linux kernel, the following vulnerability has been resolved: crypto: qat - fix VF2PF work teardown rac
CVE-2026-64270 HIGH 7.8 UPGRADE In the Linux kernel, the following vulnerability has been resolved: Input: mms114 - reject an oversized devic

References

← Back to latest CVEs