Linux: Out-of-bounds Write
CVE-2025-21734 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 c56ba3ea8e3c9a69a992aad18f7a65e43e51d623, c0464bad0e85fcd5d47e4297d1e410097c979e55, 24a79c6bc8de763f7c50f4f84f8b0c183bc25a51 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 0.2% 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 c56ba3ea8e3c9a69a992aad18f7a65e43e51d623 or c0464bad0e85fcd5d47e4297d1e410097c979e55 or 24a79c6bc8de763f7c50f4f84f8b0c183bc25a51 or c3f7161123fcbdc64e90119ccce292d8b66281c4, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.1.129 or 6.6.78 or 6.12.14 or 6.13.3, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 02b45b47fbe84e23699bb6bdc74d4c2780e282b4 up to, but not including, c56ba3ea8e3c9a69a992aad18f7a65e43e51d623; 02b45b47fbe84e23699bb6bdc74d4c2780e282b4 up to, but not including, c0464bad0e85fcd5d47e4297d1e410097c979e55; 02b45b47fbe84e23699bb6bdc74d4c2780e282b4 up to, but not including, 24a79c6bc8de763f7c50f4f84f8b0c183bc25a51; 02b45b47fbe84e23699bb6bdc74d4c2780e282b4 up to, but not including, c3f7161123fcbdc64e90119ccce292d8b66281c4; 02b45b47fbe84e23699bb6bdc74d4c2780e282b4 up to, but not including, e966eae72762ecfdbdb82627e2cda48845b9dd66; 5.2 | c56ba3ea8e3c9a69a992aad18f7a65e43e51d623, c0464bad0e85fcd5d47e4297d1e410097c979e55, 24a79c6bc8de763f7c50f4f84f8b0c183bc25a51, c3f7161123fcbdc64e90119ccce292d8b66281c4, e966eae72762ecfdbdb82627e2cda48845b9dd66 |
| Linux | Linux Kernel | 5.2 up to, but not including, 6.1.129; 6.2 up to, but not including, 6.6.78; 6.7 up to, but not including, 6.12.14; 6.13 up to, but not including, 6.13.3 | 6.1.129, 6.6.78, 6.12.14, 6.13.3 |
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 |
Official description
In the Linux kernel, the following vulnerability has been resolved: misc: fastrpc: Fix copy buffer page size For non-registered buffer, fastrpc driver copies the buffer and pass it to the remote subsystem. There is a problem with current implementation of page size calculation which is not considering the offset in the calculation. This might lead to passing of improper and out-of-bounds page size which could result in memory issue. Calculate page start and page end using the offset adjusted address instead of absolute address.
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.
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/24a79c6bc8de763f7c50f4f84f8b0c183bc25a51
- git.kernel.org/stable/c/c0464bad0e85fcd5d47e4297d1e410097c979e55
- git.kernel.org/stable/c/c3f7161123fcbdc64e90119ccce292d8b66281c4
- git.kernel.org/stable/c/c56ba3ea8e3c9a69a992aad18f7a65e43e51d623
- git.kernel.org/stable/c/e966eae72762ecfdbdb82627e2cda48845b9dd66
Other references
Recent Out-of-bounds Write vulnerabilities
- 9.8 Critical severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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