Linux: Out-of-bounds Write
CVE-2025-21919 is a high-severity out-of-bounds write 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 5cb300dcdd27e6a351ac02541e0231261c775852, 000c9ee43928f2ce68a156dd40bab7616256f4dd, 9cc7f0018609f75a349e42e3aebc3b0e905ba775 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 0.24% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to 5cb300dcdd27e6a351ac02541e0231261c775852 or 000c9ee43928f2ce68a156dd40bab7616256f4dd or 9cc7f0018609f75a349e42e3aebc3b0e905ba775 or b5741e4b9ef3567613b2351384f91d3f16e59986, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.15.179 or 6.1.131 or 6.6.83 or 6.12.19, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | fdaba61ef8a268d4136d0a113d153f7a89eb9984 up to, but not including, 5cb300dcdd27e6a351ac02541e0231261c775852; fdaba61ef8a268d4136d0a113d153f7a89eb9984 up to, but not including, 000c9ee43928f2ce68a156dd40bab7616256f4dd; fdaba61ef8a268d4136d0a113d153f7a89eb9984 up to, but not including, 9cc7f0018609f75a349e42e3aebc3b0e905ba775; fdaba61ef8a268d4136d0a113d153f7a89eb9984 up to, but not including, b5741e4b9ef3567613b2351384f91d3f16e59986; fdaba61ef8a268d4136d0a113d153f7a89eb9984 up to, but not including, e1dd09df30ba86716cb2ffab97dc35195c01eb8f; fdaba61ef8a268d4136d0a113d153f7a89eb9984 up to, but not including, 3b4035ddbfc8e4521f85569998a7569668cccf51; 5.13 | 5cb300dcdd27e6a351ac02541e0231261c775852, 000c9ee43928f2ce68a156dd40bab7616256f4dd, 9cc7f0018609f75a349e42e3aebc3b0e905ba775, b5741e4b9ef3567613b2351384f91d3f16e59986, e1dd09df30ba86716cb2ffab97dc35195c01eb8f, 3b4035ddbfc8e4521f85569998a7569668cccf51 |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Linux | Linux Kernel | 5.13 up to, but not including, 5.15.179; 5.16 up to, but not including, 6.1.131; 6.2 up to, but not including, 6.6.83; 6.7 up to, but not including, 6.12.19; 6.13 up to, but not including, 6.13.7; 6.14 | 5.15.179, 6.1.131, 6.6.83, 6.12.19, 6.13.7 |
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 NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA |
| CVSS 3.1 | 7.8 | High | NVD |
| CVSS 3.1 | 7.8 | High | CISA (ADP) |
Official description
In the Linux kernel, the following vulnerability has been resolved: sched/fair: Fix potential memory corruption in child_cfs_rq_on_list child_cfs_rq_on_list attempts to convert a 'prev' pointer to a cfs_rq. This 'prev' pointer can originate from struct rq's leaf_cfs_rq_list, making the conversion invalid and potentially leading to memory corruption. Depending on the relative positions of leaf_cfs_rq_list and the task group (tg) pointer within the struct, this can cause a memory fault or access garbage data. The issue arises in list_add_leaf_cfs_rq, where both cfs_rq->leaf_cfs_rq_list and rq->leaf_cfs_rq_list are added to the same leaf list. Also, rq->tmp_alone_branch can be set to rq->leaf_cfs_rq_list. This adds a check `if (prev == &rq->leaf_cfs_rq_list)` after the main conditional in child_cfs_rq_on_list. This ensures that the container_of operation will convert a correct cfs_rq struct. This check is sufficient because only cfs_rqs on the same CPU are added to the list, so verifying the 'prev' pointer against the current rq's list head is enough. Fixes a potential memory corruption issue that due to current struct layout might not be manifesting as a crash but could lead to unpredictable behavior when the layout changes.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Out-of-bounds Write
The product writes data past the end, or before the beginning, of the intended buffer.
How developers prevent this class of flaw
- Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer. Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples include the Safe C String Library (SafeStr) by Messier and Viega, and the Strsafe.h library from Microsoft. These libraries provide safer versions of overflow-prone string-handling functions.
- Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/000c9ee43928f2ce68a156dd40bab7616256f4dd
- git.kernel.org/stable/c/3b4035ddbfc8e4521f85569998a7569668cccf51
- git.kernel.org/stable/c/5cb300dcdd27e6a351ac02541e0231261c775852
- git.kernel.org/stable/c/9cc7f0018609f75a349e42e3aebc3b0e905ba775
- git.kernel.org/stable/c/b5741e4b9ef3567613b2351384f91d3f16e59986
- git.kernel.org/stable/c/e1dd09df30ba86716cb2ffab97dc35195c01eb8f
Other references
Recent Out-of-bounds Write vulnerabilities
- 9.8 Critical severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 8.1 High severity
- 7.8 High severity
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