CyberSecBulletin
CVE-2025-21764NVD status: Modified

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2025-21764 is a high-severity use after free 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 96fc896d0e5b37c12808df797397fb16f3080879, c30893ef3d9cde8e7e8e4fd06b53d2c935bbccb1, b870256dd2a5648d5ed2f22316b3ac29a7e5ed63 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 0.27% 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 96fc896d0e5b37c12808df797397fb16f3080879 or c30893ef3d9cde8e7e8e4fd06b53d2c935bbccb1 or b870256dd2a5648d5ed2f22316b3ac29a7e5ed63 or 3c2d705f5adf5d860aaef90cb4211c0fde2ba66d, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.4.291 or 5.10.235 or 5.15.179 or 6.1.129, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxde09334b9326632bbf1a74bfd8b01866cbbf2f61 up to, but not including, 96fc896d0e5b37c12808df797397fb16f3080879; de09334b9326632bbf1a74bfd8b01866cbbf2f61 up to, but not including, c30893ef3d9cde8e7e8e4fd06b53d2c935bbccb1; de09334b9326632bbf1a74bfd8b01866cbbf2f61 up to, but not including, b870256dd2a5648d5ed2f22316b3ac29a7e5ed63; de09334b9326632bbf1a74bfd8b01866cbbf2f61 up to, but not including, 3c2d705f5adf5d860aaef90cb4211c0fde2ba66d; de09334b9326632bbf1a74bfd8b01866cbbf2f61 up to, but not including, 9e0ec817eb41a55327a46cd3ce331a9868d60304; de09334b9326632bbf1a74bfd8b01866cbbf2f61 up to, but not including, bbec88e4108e8d6fb468d3817fa652140a44ff28; de09334b9326632bbf1a74bfd8b01866cbbf2f61 up to, but not including, cd1065f92eb7ff21b9ba5308a86f33d1670bf926; de09334b9326632bbf1a74bfd8b01866cbbf2f61 up to, but not including, 628e6d18930bbd21f2d4562228afe27694f66da9; and 1 more ranges96fc896d0e5b37c12808df797397fb16f3080879, c30893ef3d9cde8e7e8e4fd06b53d2c935bbccb1, b870256dd2a5648d5ed2f22316b3ac29a7e5ed63, 3c2d705f5adf5d860aaef90cb4211c0fde2ba66d, 9e0ec817eb41a55327a46cd3ce331a9868d60304, bbec88e4108e8d6fb468d3817fa652140a44ff28
SiemensSIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0)V3.1.6 and later; V3.1.7 and laterNot stated
SiemensSIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0)V3.1.6 and later; V3.1.7 and laterNot stated
SiemensSIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0)V3.1.6 and later; V3.1.7 and laterNot stated
SiemensSIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0)V3.1.6 and later; V3.1.7 and laterNot stated
SiemensSIMATIC S7-1500 TM MFP - GNU/Linux subsystemall versionsNot stated
SiemensSIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0)V3.1.6 and later; V3.1.7 and laterNot stated
LinuxLinux Kernel3.9 up to, but not including, 5.4.291; 5.5 up to, but not including, 5.10.235; 5.11 up to, but not including, 5.15.179; 5.16 up to, but not including, 6.1.129; 6.2 up to, but not including, 6.6.79; 6.7 up to, but not including, 6.12.16; 6.13 up to, but not including, 6.13.4; 6.145.4.291, 5.10.235, 5.15.179, 6.1.129, 6.6.79, 6.12.16

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.

Scoring systemScoreSeverityScored by
CVSS 3.17.8HighCNA
CVSS 3.17.8HighCISA (ADP)

Official description

In the Linux kernel, the following vulnerability has been resolved: ndisc: use RCU protection in ndisc_alloc_skb() ndisc_alloc_skb() can be called without RTNL or RCU being held. Add RCU protection to avoid possible UAF.

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

The underlying weakness: Use After Free

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.

How developers prevent this class of flaw

  • Choose a language that provides automatic memory management.
  • When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.

More Use After Free vulnerabilities (CWE-416)

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 Use After Free vulnerabilities

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