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CVE Record

CVE-2025-21637: sctp: sysctl: udp_port: avoid using current->nsproxy

In the Linux kernel, the following vulnerability has been resolved: sctp: sysctl: udp_port: 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, but that would increase the size of this fix, while 'sctp.ctl_sock' still needs to be retrieved from 'net' structure.

HighCVSS 7.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Linux kernel flaw can crash the kernel when SCTP UDP-port settings are accessed while a task is exiting. Successful local exploitation could disrupt systems or alter system behavior, but the supplied evidence indicates no confidentiality impact.

Executive priority

Prioritize remediation during the next urgent kernel-maintenance window, especially on shared Linux hosts. Accelerate internet-facing multi-user or workload-dense systems where local code execution is plausible. Treat exposure as unconfirmed until vendor package and backport checks are complete.

Technical view

The SCTP sysctl udp_port handler could dereference current->nsproxy after it becomes NULL, causing a kernel null-pointer dereference. The correction obtains the relevant network namespace from table->data instead of the current task. CVSS 3.1 is 7.1, requiring local access with low privileges and indicating high integrity and availability impact.

Likely exposure

Exposure is limited to Linux systems running affected kernel versions or branches without the referenced backports. Systems permitting untrusted local users or workloads deserve greater priority. The supplied version data is ambiguous, so distribution package status and exact backport history must determine exposure.

Exploitation context

The supplied bundle reports a syzbot-triggered kernel Oops involving an exiting task and acct(2). It does not establish malicious exploitation. The CVE is not listed as KEV, and no supplied source reports active exploitation or a public weaponized exploit.

Researcher notes

The failure is CWE-476 in SCTP sysctl handling. The unsafe dependency on current->nsproxy creates namespace inconsistency and a NULL-dereference window during task exit. The fix derives struct net through container_of() from table->data. Supplied evidence supports crash and integrity/availability risk, but not a demonstrated exploitation primitive.

Mitigation direction

  • Apply the appropriate vendor kernel update containing the referenced upstream or stable fix.
  • Consult Linux distribution guidance because patched package versions may differ from upstream kernel numbers.
  • Reboot into the updated kernel after installation.
  • Restrict unnecessary untrusted local access until affected systems are updated.

Validation and detection

  • Inventory running kernel versions, not only installed kernel packages.
  • Compare each distribution package against its vendor advisory and backport status.
  • Confirm the active kernel contains the applicable referenced fix.
  • Verify systems rebooted successfully into the patched kernel.
  • Regression-test SCTP sysctl and network-namespace operations where operationally relevant.
Prepared
Confidence
medium
Sources
8

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.

ATT&CK lookup starting points

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cwe · low confidence lookup

CWE-476: Exact CWE lookup

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cve · low confidence lookup

CVE-2025-21637 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.

2CVSS vectors
3Timeline events
2ADP providers
7Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

CVSS vector scores

2 official scores

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
5.5CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H1.83.6CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

7.1High
CVSS 3.1 vector shape for CVE-2025-21637Attack 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

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux046c052b475e7119b6a30e3483e2888fc606a2f8, 046c052b475e7119b6a30e3483e2888fc606a2f8, 046c052b475e7119b6a30e3483e2888fc606a2f8, 046c052b475e7119b6a30e3483e2888fc606a2f8, 046c052b475e7119b6a30e3483e2888fc606a2f8unaffected
LinuxLinux5.11, 0, 5.15.177, 6.1.125, 6.6.72, 6.12.10, 6.13affected
Weakness

CWE details

CWE-476

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-476 · source CWE mapping

NULL Pointer Dereference

NULL Pointer Dereference represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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