Vulnary
← back to the feed
Critical· 9.8official fix available

CVE-2025-39703

A critical bug in the Linux kernel can cause a crash when it receives a corrupted HSR frame that does not have enough space for the HSR tag. The crash occurs in the networking stack and can bring the system down. The issue is triggered by a malformed packet that can be sent over the network.

publishedSep 5, 2025
last modifiedJul 30, 2026
sourcesNVD
severity · cvss
9.8
critical · how bad it is
exploitation · epss
<1%
4th percentile · chance of exploitation in 30 days
(ai-assisted) A model wrote this summary from the official data, so double-check it against the source before you act on it. Read the official advisory →
auto-deletes from the system
counting…on Aug 29, 2026

An official fix is available, so this entry is kept for 30 days and then removed automatically.

01

Who is affected

Linux kernel versions 5.13 and 6.17 (and earlier) on systems that use HSR (High‑availability Seamless Redundancy) networking, including Debian 11.0. Any host running a vulnerable kernel and configured for HSR is at risk.

02

Real-world impact

An attacker could send a specially crafted HSR frame to a vulnerable system, causing the kernel to panic and the machine to reboot or become unresponsive. This denial‑of‑service condition could be used to disrupt critical services or as a stepping stone to further attacks if the crash can be leveraged.

03

Why this severity

The CVSS score of 9.8 reflects that the vulnerability is exploitable over the network, requires no privileges, and can compromise confidentiality, integrity, and availability, leading to a kernel panic. The attack vector is network‑based, the attack complexity is low, and the impact is complete.

04

What to do about it

official fix available
recommended steps
  1. 01Upgrade the Linux kernel to a version that includes the fix for CVE-2025-39703.
  2. 02Reboot the system to load the new kernel.

NVD-referenced vendor advisory

05

Timeline

  1. Sep 5, 2025 · Sep 5, 2025
    Published
    Disclosed and added to the National Vulnerability Database.
  2. Jul 30, 2026 · 6h ago
    Advisory updated
    The NVD record was last revised.
  3. Jul 30, 2026 · 3h ago
    Official fix available
    A vendor patch or mitigation now exists — see the remediation steps above.
06

How it’s attacked

Attack vectorNetwork (remote)
Attack complexityLow
Privileges requiredNone
User interactionNone needed
ScopeUnchanged
Confidentiality impactHigh
Integrity impactHigh
Availability impactHigh
07

References & advisories

NVD advisory ↗Search advisories ↗
(ai-assisted) A model wrote this summary from the official data, so double-check it against the source before you act on it. Read the official advisory →