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CVE Record

CVE-2025-37797: net_sched: hfsc: Fix a UAF vulnerability in class handling

In the Linux kernel, the following vulnerability has been resolved: net_sched: hfsc: Fix a UAF vulnerability in class handling This patch fixes a Use-After-Free vulnerability in the HFSC qdisc class handling. The issue occurs due to a time-of-check/time-of-use condition in hfsc_change_class() when working with certain child qdiscs like netem or codel. The vulnerability works as follows: 1. hfsc_change_class() checks if a class has packets (q.qlen != 0) 2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g., codel, netem) might drop packets and empty the queue 3. The code continues assuming the queue is still non-empty, adding the class to vttree 4. This breaks HFSC scheduler assumptions that only non-empty classes are in vttree 5. Later, when the class is destroyed, this can lead to a Use-After-Free The fix adds a second queue length check after qdisc_peek_len() to verify the queue wasn't emptied.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A flaw in Linux traffic scheduling can leave freed kernel memory referenced after an HFSC queue changes unexpectedly. A local attacker meeting the required access conditions could potentially crash the system or affect confidentiality and integrity. Exposure is configuration-dependent, and the supplied sources do not establish active exploitation.

Executive priority

Treat as a high-priority, configuration-dependent kernel update. Accelerate remediation for shared, multi-user, container-hosting, or otherwise locally exposed systems using HFSC. Other systems should follow normal expedited kernel patching after confirming vendor applicability. No supplied evidence supports declaring an active emergency exploitation campaign.

Technical view

A time-of-check/time-of-use flaw exists in hfsc_change_class(). After confirming a class queue is non-empty, qdisc_peek_len() may cause child qdiscs such as codel or netem to drop the remaining packets. The class can then be incorrectly inserted into vttree, violating HFSC assumptions and enabling a later use-after-free during class destruction. The fix rechecks queue length after peeking.

Likely exposure

Potentially exposed systems run an affected Linux kernel and use HFSC with relevant child qdiscs, including codel or netem. The CVSS vector describes local, low-privilege attack access. Internet reachability alone does not establish exposure. The supplied affected-version data is ambiguous, so distribution-specific kernel status should be verified.

Exploitation context

The CVSS 3.1 score is 7.8, with local access, low complexity, low privileges, no user interaction, and potentially high confidentiality, integrity, and availability impact. The bundle marks this CVE as absent from KEV and provides no evidence of exploitation in the wild or a public exploit.

Researcher notes

The supplied version list appears flattened and does not clearly distinguish introduction points from fixed boundaries. Do not infer exact vulnerable ranges from it alone. The described corruption requires HFSC state plus a child qdisc whose peek operation can empty the queue. Stable-kernel commits and Debian advisories provide remediation anchors, but the bundle does not document exploit reproducibility.

Mitigation direction

  • Update to a vendor-supported kernel that incorporates the referenced stable fix.
  • Consult the Linux distribution's advisory to map fixed packages to deployed kernel versions.
  • Prioritize multi-user or tenant systems where untrusted users may reach local kernel networking functionality.
  • Where operationally feasible, avoid affected HFSC child-qdisc combinations until patched.

Validation and detection

  • Inventory kernel versions across Linux hosts and compare them with vendor advisories.
  • Identify systems configured with HFSC and child qdiscs such as codel or netem.
  • Confirm the installed kernel package includes the referenced upstream correction.
  • Reboot updated systems when required, then verify the running kernel version.
  • Monitor vendor advisories for corrected affected-version boundaries or revised exploitation information.
Prepared
Confidence
medium
Sources
6

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

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CVE-2025-37797 mapping review

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Vulnerability profileCVE Program record
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

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

SSVC decision data

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

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
7.8CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2025-37797Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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
CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14, 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14, 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14, 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14, 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14, 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14, 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14, 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14unaffected
LinuxLinux4.14, 0, 5.4.293, 5.10.237, 5.15.181, 6.1.136, 6.6.89, 6.12.26, 6.14.5, 6.15affected
Weakness

CWE details

No CWE listed

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