CyberSecBulletin
CVE-2025-21647NVD status: Modified

Linux: Out-of-bounds Read

Published Updated By the CyberSecBulletin desk

CVE-2025-21647 is a high-severity out-of-bounds read vulnerability in Linux, with a CVSS 3.1 base score of 7.1 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 44fe1efb4961c1a5ccab16bb579dfc6b308ad58b, b1a1743aaa4906c41c426eda97e2e2586f79246d, bb0245fa72b783cb23a9949c5048781341e91423 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 0.28% 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 44fe1efb4961c1a5ccab16bb579dfc6b308ad58b or b1a1743aaa4906c41c426eda97e2e2586f79246d or bb0245fa72b783cb23a9949c5048781341e91423 or a777e06dfc72bed73c05dcb437d7c27ad5f90f3f, 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 6.1.125, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux4a4eeefa514db570be025ab46d779af180e2c9bb up to, but not including, 44fe1efb4961c1a5ccab16bb579dfc6b308ad58b; 7725152b54d295b7da5e34c2f419539b30d017bd up to, but not including, b1a1743aaa4906c41c426eda97e2e2586f79246d; cde71a5677971f4f1b69b25e854891dbe78066a4 up to, but not including, bb0245fa72b783cb23a9949c5048781341e91423; 549e407569e08459d16122341d332cb508024094 up to, but not including, a777e06dfc72bed73c05dcb437d7c27ad5f90f3f; d4a9039a7b3d8005b90c7b1a55a306444f0e5447 up to, but not including, 27202e2e8721c3b23831563c36ed5ac7818641ba; 546ea84d07e3e324644025e2aae2d12ea4c5896e up to, but not including, 91bb18950b88f955838ec0c1d97f74d135756dc7; 546ea84d07e3e324644025e2aae2d12ea4c5896e up to, but not including, 737d4d91d35b5f7fa5bb442651472277318b0bfd; d7c01c0714c04431b5e18cf17a9ea68a553d1c3c; and 7 more ranges44fe1efb4961c1a5ccab16bb579dfc6b308ad58b, b1a1743aaa4906c41c426eda97e2e2586f79246d, bb0245fa72b783cb23a9949c5048781341e91423, a777e06dfc72bed73c05dcb437d7c27ad5f90f3f, 27202e2e8721c3b23831563c36ed5ac7818641ba, 91bb18950b88f955838ec0c1d97f74d135756dc7
SiemensSIMATIC S7-1500 TM MFP - BIOSall versionsNot stated
SiemensSIMATIC S7-1500 TM MFP - GNU/Linux subsystemall versionsNot stated
LinuxLinux Kernel5.4.284 up to, but not including, 5.4.291; 5.10.226 up to, but not including, 5.10.235; 5.15.167 up to, but not including, 5.15.179; 6.1.110 up to, but not including, 6.1.125; 6.6.51 up to, but not including, 6.6.72; 6.10.10 up to, but not including, 6.11; 6.11.1 up to, but not including, 6.12.10; 6.11; and 1 more ranges5.4.291, 5.10.235, 5.15.179, 6.1.125, 6.6.72, 6.11

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
NoneNothing can be modified.
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:N/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.17.3HighCNA
CVSS 3.17.1HighNVD

Official description

In the Linux kernel, the following vulnerability has been resolved: sched: sch_cake: add bounds checks to host bulk flow fairness counts Even though we fixed a logic error in the commit cited below, syzbot still managed to trigger an underflow of the per-host bulk flow counters, leading to an out of bounds memory access. To avoid any such logic errors causing out of bounds memory accesses, this commit factors out all accesses to the per-host bulk flow counters to a series of helpers that perform bounds-checking before any increments and decrements. This also has the benefit of improving readability by moving the conditional checks for the flow mode into these helpers, instead of having them spread out throughout the code (which was the cause of the original logic error). As part of this change, the flow quantum calculation is consolidated into a helper function, which means that the dithering applied to the ost load scaling is now applied both in the DRR rotation and when a sparse flow's quantum is first initiated. The only user-visible effect of this is that the maximum packet size that can be sent while a flow stays sparse will now vary with +/- one byte in some cases. This should not make a noticeable difference in practice, and thus it's not worth complicating the code to preserve the old behaviour.

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

The underlying weakness: Out-of-bounds Read

The product reads data past the end, or before the beginning, of the intended buffer.

How developers prevent this class of flaw

  • Use a language that provides appropriate memory abstractions.

More Out-of-bounds Read vulnerabilities (CWE-125)

Timeline

  1. CVE record published.
  2. Record last changed materially (score, affected products, status or references).

References

Recent Out-of-bounds Read vulnerabilities

Spotted an error? Tell us.