Vulnary
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Critical· 9.8official fix available

CVE-2025-40257

A race condition in the Linux kernel’s MPTCP implementation can cause a use‑after‑free error, potentially crashing the system or allowing arbitrary code execution. The flaw occurs when a timer is stopped while its data structure is freed. The issue has been fixed by adding RCU protection to the timer handling code.

publishedDec 4, 2025
last modifiedJul 30, 2026
sourcesNVD
severity · cvss
9.8
critical · how bad it is
exploitation · epss
<1%
7th 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, any version before the patch that adds RCU protection to mptcp_pm_del_add_timer()

02

Real-world impact

An attacker could crash the system or run arbitrary code by exploiting the use‑after‑free in the MPTCP subsystem.

03

Why this severity

The CVSS score of 9.8 reflects the high impact on confidentiality, integrity, and availability, and the fact that the vulnerability can be exploited remotely without authentication or user interaction.

04

What to do about it

official fix available
recommended steps
  1. 011. Update your Linux kernel to a version that includes the mptcp_pm_del_add_timer RCU protection fix.
  2. 022. Reboot the system to load the updated kernel.

NVD-referenced vendor advisory

05

Timeline

  1. Dec 4, 2025 · Dec 4, 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 →