CVE-2025-21734 [High] | Out-of-bounds Write in Linux Kernel

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.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.01%	0.19%	+0.18%
2	2026-05-09	0.06%	0.01%	-0.05%
3	2026-04-07	—	0.06%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.01%

0.19%

+0.18%

2026-05-09

0.06%

0.01%

-0.05%

2026-04-07

—

0.06%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
7.8	3.1	HIGH	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:L) They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:L) A normal user session is enough; they don’t have to be admin. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	1.8	5.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

7.8

3.1

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand

Attack vector (AV:L): They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L): A normal user session is enough; they don’t have to be admin.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

1.8

5.9

[email protected]

OS Trackers for CVE-2025-21734

vendor	priority	summary	link
`debian`	not yet assigned	CVE-2025-21734 not yet assigned priority: Debian including 2 source packages (linux, linux-6.1), 6 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5, open 1.	https://security-tracker.debian.org/tracker/CVE-2025-21734
`redhat`	—	—	https://access.redhat.com/security/cve/CVE-2025-21734
`suse`	medium	CVE-2025-21734 severity moderate: SUSE including 415 source package names (2.1.3-6.11:kernel-default-6.4.0-28.1, 2.1.3-6.12:kernel-default-base-6.4.0-28.1.21.6, …), 661 product×package rows across 115 product lines (Container suse/sl-micro/6.0/base-os-container, Container suse/sl-micro/6.0/kvm-os-container, … (115 product lines)): Fixed 361, Known Affected 231, Known Not Affected 69.	https://www.suse.com/security/cve/CVE-2025-21734/
`ubuntu`	medium	CVE-2025-21734 medium priority: Ubuntu including 158 source packages (linux, linux-allwinner-5.19, …), 1551 status rows across 10 suites (bionic, focal, jammy, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 1145, ignored 148, released 136, not-affected 67, needed 55.	https://ubuntu.com/security/CVE-2025-21734

Affected software / configurations for CVE-2025-21734

Vendor	Product	Version	Raw CPE
linux	linux_kernel	>= 5.2, < 6.1.129	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.2, < 6.6.78	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.7, < 6.12.14	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.13, < 6.13.3	cpe:2.3:o:linux:linux_kernel::::::::

References for CVE-2025-21734

URL	Tags
https://git.kernel.org/stable/c/24a79c6bc8de763f7c50f4f84f8b0c183bc25a51	Patch
https://git.kernel.org/stable/c/c0464bad0e85fcd5d47e4297d1e410097c979e55	Patch
https://git.kernel.org/stable/c/c3f7161123fcbdc64e90119ccce292d8b66281c4	Patch
https://git.kernel.org/stable/c/c56ba3ea8e3c9a69a992aad18f7a65e43e51d623	Patch
https://git.kernel.org/stable/c/e966eae72762ecfdbdb82627e2cda48845b9dd66	Patch
https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html

URL

CVE-2025-21734 | misc: fastrpc: Fix copy buffer page size

Exploit prediction scoring system (EPSS) score for CVE-2025-21734

Common vulnerability scoring system (CVSS) metrics for CVE-2025-21734

Weakness enumeration for CVE-2025-21734

OS Trackers for CVE-2025-21734

Affected software / configurations for CVE-2025-21734

References for CVE-2025-21734