Security readout for executives and security teams
Plain-English summary
A Linux kernel FastRPC buffer-copy error can calculate an incorrect page size, potentially causing out-of-bounds memory access. A local user with limited privileges may be able to trigger serious confidentiality, integrity, or availability impacts. Exposure depends on whether an affected kernel and the relevant FastRPC functionality are present and usable.
Executive priority
Prioritize affected multi-user systems, appliances, and environments where untrusted local accounts can reach FastRPC. Schedule prompt vendor-supported kernel updates. Emergency treatment is appropriate where exposure is confirmed and business-critical, but the supplied evidence does not establish active exploitation.
Technical view
For non-registered FastRPC buffers, page-size calculation failed to account correctly for the buffer offset. The driver could therefore pass an invalid, out-of-bounds page size to a remote subsystem, creating a kernel memory-safety condition. Stable-kernel commits correct the calculation by deriving page boundaries from the offset-adjusted address.
Likely exposure
Potentially exposed systems run an affected Linux kernel and make the FastRPC driver available to local, low-privileged users. The supplied version data includes Linux 5.2 and later release entries, but does not provide sufficiently clear ranges for reliable version-only conclusions. Confirm against distribution or vendor package guidance and the cited fixes.
Exploitation context
The supplied CVSS 3.1 score is 7.8, with local access, low complexity, low privileges, no user interaction, and potentially high impact. The bundle marks KEV false, and no cited source reports active exploitation or a public exploit. Treat exploitation status as unconfirmed, not impossible.
Researcher notes
The record attributes the flaw to offset-insensitive page-boundary calculation for copied, non-registered buffers. Five stable commits are cited, indicating fixes across kernel branches. The supplied affected-version representation is ambiguous, and no CWE, crash trace, exploit evidence, or branch-to-fixed-version mapping is provided; validate using authoritative package metadata.
Mitigation direction
- Install a vendor-supported kernel package containing the applicable stable fix.
- Check distribution or device-vendor guidance for exact affected and corrected versions.
- Restrict unnecessary local access while remediation is pending.
- Disable unused FastRPC functionality only when vendor guidance confirms operational safety.
Validation and detection
- Inventory kernel versions across Linux systems and appliances.
- Determine whether the FastRPC driver is built, loaded, or otherwise available.
- Compare kernel source or package changelogs with the cited stable fix commits.
- Verify the running kernel after remediation, including completion of any required reboot.
- Review kernel logs for related memory faults; absence does not prove non-exposure.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CVE-2025-21734 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9LinuxVulnerability scoring details
Base CVSS 3.1 score
7.8HighVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://git.kernel.org/stable/c/c56ba3ea8e3c9a69a992aad18f7a65e43e51d623CVE reference, Linux
- https://git.kernel.org/stable/c/c0464bad0e85fcd5d47e4297d1e410097c979e55CVE reference, Linux
- https://git.kernel.org/stable/c/24a79c6bc8de763f7c50f4f84f8b0c183bc25a51CVE reference, Linux
- https://git.kernel.org/stable/c/c3f7161123fcbdc64e90119ccce292d8b66281c4CVE reference, Linux
- https://git.kernel.org/stable/c/e966eae72762ecfdbdb82627e2cda48845b9dd66CVE reference, Linux
- https://lists.debian.org/debian-lts-announce/2025/03/msg00028.htmlCVE reference, CVE
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.