CyberSecBulletin
CVE-2026-63971NVD status: Modified

Linux: Concurrent Execution using Shared Resource with Improper Synchronization

Published Updated By the CyberSecBulletin desk

CVE-2026-63971 is a high-severity concurrent execution using shared resource with improper synchronization vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 0e0d5bc76fd4267a71334fcc8f1a5fbcf997845d, bcfeac79af740735ace44008b4a11b8e5add20f5, 8e9b56051d24540cfbf39194618708c4a7633549 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.13% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to 0e0d5bc76fd4267a71334fcc8f1a5fbcf997845d or bcfeac79af740735ace44008b4a11b8e5add20f5 or 8e9b56051d24540cfbf39194618708c4a7633549 or 634a9af8a26a84d8b0d7b3b643204b344b42d9fb, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.10.259 or 5.15.210 or 6.1.176 or 6.6.143, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux668c9beb9020d5834ee9e43c208190a07d2b1928 up to, but not including, 0e0d5bc76fd4267a71334fcc8f1a5fbcf997845d; 668c9beb9020d5834ee9e43c208190a07d2b1928 up to, but not including, bcfeac79af740735ace44008b4a11b8e5add20f5; 668c9beb9020d5834ee9e43c208190a07d2b1928 up to, but not including, 8e9b56051d24540cfbf39194618708c4a7633549; 668c9beb9020d5834ee9e43c208190a07d2b1928 up to, but not including, 634a9af8a26a84d8b0d7b3b643204b344b42d9fb; 668c9beb9020d5834ee9e43c208190a07d2b1928 up to, but not including, 7d2038d4b80166f7bead8d07eba3b97405816c21; 668c9beb9020d5834ee9e43c208190a07d2b1928 up to, but not including, 68667ee4c7dadf7f63167234e2a1af09b3f7874e; 668c9beb9020d5834ee9e43c208190a07d2b1928 up to, but not including, 6140cfa721451fa6e18e134e709703c2bf34d0fb; 668c9beb9020d5834ee9e43c208190a07d2b1928 up to, but not including, f14fe6395a8b3d961a61e138ad7b36ba3626dd4e; and 1 more ranges0e0d5bc76fd4267a71334fcc8f1a5fbcf997845d, bcfeac79af740735ace44008b4a11b8e5add20f5, 8e9b56051d24540cfbf39194618708c4a7633549, 634a9af8a26a84d8b0d7b3b643204b344b42d9fb, 7d2038d4b80166f7bead8d07eba3b97405816c21, 68667ee4c7dadf7f63167234e2a1af09b3f7874e
LinuxLinux Kernel4.16 up to, but not including, 5.10.259; 5.11 up to, but not including, 5.15.210; 5.16 up to, but not including, 6.1.176; 6.2 up to, but not including, 6.6.143; 6.7 up to, but not including, 6.12.93; 6.13 up to, but not including, 6.18.35; 6.19 up to, but not including, 7.0.12; 7.15.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93, 6.18.35

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: sctp: fix race between sctp_wait_for_connect and peeloff sctp_wait_for_connect() drops and re-acquires the socket lock while waiting for the association to reach ESTABLISHED state. During this window, another thread can peeloff the association to a new socket via getsockopt(SCTP_SOCKOPT_PEELOFF), changing asoc->base.sk. After re-acquiring the old socket lock, sctp_wait_for_connect() returns success without noticing the migration — the caller then accesses the association under the wrong lock in sctp_datamsg_from_user(). Add the same sk != asoc->base.sk check that sctp_wait_for_sndbuf() already has, returning an error if the association was migrated while we slept.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Concurrent Execution using Shared Resource with Improper Synchronization

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

How developers prevent this class of flaw

  • In languages that support it, use synchronization primitives. Only wrap these around critical code to minimize the impact on performance.
  • Use thread-safe capabilities such as the data access abstraction in Spring.
  • Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring. Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

More Concurrent Execution using Shared Resource with Improper Synchronization vulnerabilities (CWE-362)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Concurrent Execution using Shared Resource with Improper Synchronization vulnerabilities

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