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CVE Record

CVE-2025-21640: sctp: sysctl: cookie_hmac_alg: avoid using current->nsproxy

In the Linux kernel, the following vulnerability has been resolved: sctp: sysctl: cookie_hmac_alg: avoid using current->nsproxy As mentioned in a previous commit of this series, using the 'net' structure via 'current' is not recommended for different reasons: - Inconsistency: getting info from the reader's/writer's netns vs only from the opener's netns. - current->nsproxy can be NULL in some cases, resulting in an 'Oops' (null-ptr-deref), e.g. when the current task is exiting, as spotted by syzbot [1] using acct(2). The 'net' structure can be obtained from the table->data using container_of(). Note that table->data could also be used directly, as this is the only member needed from the 'net' structure, but that would increase the size of this fix, to use '*data' everywhere 'net->sctp.sctp_hmac_alg' is used.

HighCVSS 7.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A flaw in the Linux kernel’s SCTP configuration handling can dereference missing task namespace data and crash the kernel. Exploitation requires local, low-privileged access, but successful triggering could seriously disrupt affected systems and potentially affect integrity, according to the supplied CVSS assessment.

Executive priority

Treat this as a high-priority kernel maintenance issue, especially on multi-user or shared Linux systems. It is not documented as remotely exploitable or actively exploited, so emergency internet-edge response is unsupported. Accelerate normal patching where untrusted local users, workloads, or tenants can interact with the host kernel.

Technical view

The SCTP cookie_hmac_alg sysctl handler improperly accessed networking namespace state through current->nsproxy. That pointer can be NULL while a task is exiting, causing a kernel null-pointer dereference. Stable fixes obtain the namespace from table->data instead. The supplied CVSS 3.1 score is 7.1, with local attack vector, low complexity, low privileges, and high integrity and availability impacts.

Likely exposure

Exposure is limited to Linux systems running affected kernel builds where a local, low-privileged user can reach the vulnerable SCTP sysctl behavior. The bundle lists affected releases from 3.8 through 6.13, but its flattened version data does not provide reliable distribution-specific boundaries. Confirm status using kernel and operating-system vendor advisories.

Exploitation context

The issue was found by syzbot in a task-exit scenario involving acct(2). The supplied record is not in KEV and provides no evidence of active exploitation. It also does not establish whether practical impact beyond a kernel crash has been demonstrated.

Researcher notes

The documented fault is a current->nsproxy lifetime/context error in the SCTP cookie_hmac_alg sysctl path. The fix changes namespace lookup to derive net from table->data. Although the CVSS vector assigns high integrity and availability impact, the narrative directly demonstrates a null dereference and kernel Oops; stronger integrity impact is not explained. Exact affected-to-fixed version mapping remains incomplete in the supplied bundle.

Mitigation direction

  • Install a vendor-supported kernel containing the applicable stable fix.
  • Review Linux distribution advisories for corrected package versions.
  • Prioritize shared, multi-user, and other locally accessible systems.
  • Restrict unnecessary local account access while patching is pending.

Validation and detection

  • Inventory Linux kernel versions and map them to vendor advisories.
  • Confirm the installed kernel includes the applicable stable fix.
  • Identify systems using or exposing SCTP configuration interfaces.
  • Review kernel logs for SCTP, nsproxy, null-pointer, or Oops events.
  • Validate updated kernels in staging before production rollout.
Prepared
Confidence
medium
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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.

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CVE-2025-21640 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.1 (3.1)
Known Exploited
No
Published

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

Official CVE source material

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.

1CVSS vectors
3Timeline events
2ADP providers
11Source links

CVSS vector scores

1 official score

We 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.

ScoreVersionSeverityVectorExploitImpactSource
7.1CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H1.85.2Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.1High
CVSS 3.1 vector shape for CVE-2025-21640Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CVECVE Program Container
siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux3c68198e75111a905ac2412be12bf7b29099729b, 3c68198e75111a905ac2412be12bf7b29099729b, 3c68198e75111a905ac2412be12bf7b29099729b, 3c68198e75111a905ac2412be12bf7b29099729b, 3c68198e75111a905ac2412be12bf7b29099729b, 3c68198e75111a905ac2412be12bf7b29099729b, 3c68198e75111a905ac2412be12bf7b29099729bunaffected
LinuxLinux3.8, 0, 5.4.292, 5.10.234, 5.15.177, 6.1.125, 6.6.72, 6.12.10, 6.13affected
Weakness

CWE details

No CWE listed

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