Security readout for executives and security teams
Plain-English summary
CVE-2025-21844 is a Linux kernel SMB client flaw that can crash affected systems through a null pointer dereference. The impact is availability, not data theft or tampering. The CVSS score is 5.5, and the source bundle does not show active exploitation or CISA KEV listing.
Executive priority
Schedule remediation through normal kernel patch cycles, with faster handling for shared systems, multi-user servers, and environments where local users are less trusted. This is not currently supported as an emergency internet-scale issue by the supplied evidence.
Technical view
The Linux SMB client function receive_encrypted_standard() did not check whether cifs_buf_get() or cifs_small_buf_get() returned a valid buffer. A failed allocation could lead to a null pointer dereference. The fix adds return-value checks for next_buffer handling in upstream stable commits.
Likely exposure
Exposure is most relevant to Linux systems using the kernel SMB/CIFS client on affected kernel branches or vendor builds. The CVSS vector indicates local access with low privileges is required and the expected impact is high availability loss only.
Exploitation context
The provided sources identify this as a local, low-complexity availability issue. CISA KEV is false, and the bundle provides no evidence of public exploitation. Treat exploitation status as unconfirmed unless vendor or threat-intelligence sources say otherwise.
Researcher notes
The root issue is CWE-476 in Linux SMB client encrypted receive handling. The source bundle names upstream stable commits and downstream Debian and Siemens advisories, but does not include exploit details, proof-of-concept status, or full product matrices beyond those references.
Mitigation direction
- Apply Linux kernel updates that include the referenced upstream stable fixes.
- Follow Debian LTS advisories if running affected Debian kernel packages.
- Check Siemens SSA-265688 for product-specific exposure and remediation.
- Prioritize systems where untrusted local users can access SMB client functionality.
- If updates are unavailable, follow vendor guidance for temporary risk reduction.
Validation and detection
- Inventory Linux kernel versions and vendor kernel package builds.
- Identify hosts using SMB/CIFS client functionality or mounts.
- Compare installed kernels against the CVE affected and fixed version data.
- Confirm vendor advisories or changelogs reference CVE-2025-21844 or the stable commits.
- After patching, verify the updated kernel is booted, not only installed.
Public sources used
- CVE Program
- CVE List V5
- Linux stable commit f277e479
- Linux stable commit f618aeb6
- Linux stable commit 24e8e452
- Linux stable commit 9e5d99a4
- Linux stable commit a9b0b4b2
- Linux stable commit 554736b5
- Linux stable commit 860ca5e5
- Debian LTS advisory May 2025 msg00045
- Debian LTS advisory May 2025 msg00030
- Siemens SSA-265688
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.
CWE-476: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2025-21844 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
- Medium
- CVSS
- 5.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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.
SSVC decision data
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:N/I:N/A:H1.83.6CISA-ADPVulnerability scoring details
Base CVSS 3.1 score
5.5MediumVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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/f277e479eea3d1aa18bc712abe1d2bf3dece2e30CVE reference, Linux
- https://git.kernel.org/stable/c/f618aeb6cad2307e48a641379db610abcf593edfCVE reference, Linux
- https://git.kernel.org/stable/c/24e8e4523d3071bc5143b0db9127d511489f7b3bCVE reference, Linux
- https://git.kernel.org/stable/c/9e5d99a4cf2e23c716b44862975548415fae5391CVE reference, Linux
- https://git.kernel.org/stable/c/a9b0b4b29877cb4dc5d0842b59b5ccbacddb85bdCVE reference, Linux
- https://git.kernel.org/stable/c/554736b583f529ee159aa95af9a0cbc12b5ffc96CVE reference, Linux
- https://git.kernel.org/stable/c/860ca5e50f73c2a1cef7eefc9d39d04e275417f7CVE reference, Linux
- https://lists.debian.org/debian-lts-announce/2025/05/msg00045.htmlCVE reference, CVE
- https://lists.debian.org/debian-lts-announce/2025/05/msg00030.htmlCVE reference, CVE
- https://cert-portal.siemens.com/productcert/html/ssa-265688.htmlCVE reference, siemens-SADP
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.
NULL Pointer Dereference
NULL Pointer Dereference represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.