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CVE-2025-21702· NVD / CVE Program· CNA Linux

pfifo_tail_enqueue: Drop new packet when sch->limit == 0

In the Linux kernel, the following vulnerability has been resolved: pfifo_tail_enqueue: Drop new packet when sch->limit == 0 Expected behaviour: In case we reach scheduler's limit, pfifo_tail_enqueue() will drop a packet in scheduler's queue and decrease scheduler's qlen by one. Then, pfifo_tail_enqueue() enqueue new packet and increase scheduler's qlen by one. Finally, pfifo_tail_enqueue() return `NET_XMIT_CN` status code. Weird behaviour: In case we set `sch->limit == 0` and trigger pfifo_tail_enqueue() on a scheduler that has no packet, the 'drop a packet' step will do nothing. This means the scheduler's qlen still has value equal 0. Then, we continue to enqueue new packet and increase scheduler's qlen by one. In summary, we can leverage pfifo_tail_enqueue() to increase qlen by one and return `NET_XMIT_CN` status code. The problem is: Let's say we have two qdiscs: Qdisc_A and Qdisc_B. - Qdisc_A's type must have '->graft()' function to create parent/child relationship. Let's say Qdisc_A's type is `hfsc`. Enqueue packet to this qdisc will trigger `hfsc_enqueue`. - Qdisc_B's type is pfifo_head_drop. Enqueue packet to this qdisc will trigger `pfifo_tail_enqueue`. - Qdisc_B is configured to have `sch->limit == 0`. - Qdisc_A is configured to route the enqueued's packet to Qdisc_B. Enqueue packet through Qdisc_A will lead to: - hfsc_enqueue(Qdisc_A) -> pfifo_tail_enqueue(Qdisc_B) - Qdisc_B->q.qlen += 1 - pfifo_tail_enqueue() return `NET_XMIT_CN` - hfsc_enqueue() check for `NET_XMIT_SUCCESS` and see `NET_XMIT_CN` => hfsc_enqueue() don't increase qlen of Qdisc_A. The whole process lead to a situation where Qdisc_A->q.qlen == 0 and Qdisc_B->q.qlen == 1. Replace 'hfsc' with other type (for example: 'drr') still lead to the same problem. This violate the design where parent's qlen should equal to the sum of its childrens'qlen. Bug impact: This issue can be used for user->kernel privilege escalation when it is reachable.

HighCVSS 7.0 · v3.1—No exploit Fix available
Published
Feb 18, 2025
Updated
Sep 8, 2026
EPSS
0.3% · 18th percentile
CWE
—
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JSON

Action score

28

Monitor

Low priority for now.

CVSS
28 / 40 · 7.0 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.3%

CNA vs NVD score

NVD
7.0
CNA · Linux
7.8
0.8 point gap

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Affected systems

VendorProduct
linuxlinux kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel2.6.34 and later · before 5.4.291
  • linux linux kernel5.5 and later · before 5.10.235
  • linux linux kernel5.11 and later · before 5.15.179
  • linux linux kernel5.16 and later · before 6.1.130
  • linux linux kernel6.2 and later · before 6.6.83
  • linux linux kernel6.7 and later · before 6.12.14
  • linux linux kernel6.13 and later · before 6.13.3
  • linux linux kernel6.14

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 2.6.34affected
    • 57dbb2d83d100ea601c54fe129bfde0678db5dee and later · before 78285b53266d6d51fa4ff504a23df03852eba84eaffected · git
    • 57dbb2d83d100ea601c54fe129bfde0678db5dee and later · before 7a9723ec27aff5674f1fd4934608937f1d650980affected · git
    • 57dbb2d83d100ea601c54fe129bfde0678db5dee and later · before a56a6e8589a9b98d8171611fbcc1e45a15fd2455affected · git
    • 57dbb2d83d100ea601c54fe129bfde0678db5dee and later · before 020ecb76812a0526f4130ab5aeb6dc7c773e7ab9affected · git
    • 57dbb2d83d100ea601c54fe129bfde0678db5dee and later · before 79a955ea4a2e5ddf4a36328959de0de496419888affected · git
    • 57dbb2d83d100ea601c54fe129bfde0678db5dee and later · before e40cb34b7f247fe2e366fd192700d1b4f38196caaffected · git
    • 57dbb2d83d100ea601c54fe129bfde0678db5dee and later · before b6a079c3b6f95378f26e2aeda520cb3176f7067baffected · git
    • 57dbb2d83d100ea601c54fe129bfde0678db5dee and later · before 647cef20e649c576dff271e018d5d15d998b629daffected · git
    • before 2.6.34not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 6.1.133-16.1.133-1
Debian:13linuxbefore 6.12.15-16.12.15-1
openSUSE:Leap 15.6dtb-aarch64before 6.4.0-150600.23.53.16.4.0-150600.23.53.1
openSUSE:Leap 15.6kernel-debugbefore 6.4.0-150600.23.53.16.4.0-150600.23.53.1
openSUSE:Leap 15.6kernel-kvmsmallbefore 6.4.0-150600.23.53.16.4.0-150600.23.53.1
openSUSE:Leap 15.6kernel-obs-qabefore 6.4.0-150600.23.53.16.4.0-150600.23.53.1
SUSE:Linux Enterprise Live Patching 12 SP5kgraft-patch-SLE12-SP5_Update_58before 15-2.115-2.1
SUSE:Linux Enterprise Live Patching 12 SP5kgraft-patch-SLE12-SP5_Update_60before 13-2.113-2.1
SUSE:Linux Enterprise Live Patching 12 SP5kgraft-patch-SLE12-SP5_Update_61before 12-2.112-2.1
SUSE:Linux Enterprise Live Patching 12 SP5kgraft-patch-SLE12-SP5_Update_64before 7-2.17-2.1
SUSE:Linux Enterprise Live Patching 12 SP5kgraft-patch-SLE12-SP5_Update_66before 5-2.15-2.1
SUSE:Linux Enterprise Live Patching 12 SP5kgraft-patch-SLE12-SP5_Update_68before 2-2.12-2.1
SUSE:Linux Enterprise Live Patching 15 SP3kernel-livepatch-SLE15-SP3_Update_46before 17-150300.2.117-150300.2.1
SUSE:Linux Enterprise Live Patching 15 SP3kernel-livepatch-SLE15-SP3_Update_47before 15-150300.2.115-150300.2.1
SUSE:Linux Enterprise Live Patching 15 SP3kernel-livepatch-SLE15-SP3_Update_48before 14-150300.2.114-150300.2.1
SUSE:Linux Enterprise Live Patching 15 SP3kernel-livepatch-SLE15-SP3_Update_50before 11-150300.2.111-150300.2.1
SUSE:Linux Enterprise Live Patching 15 SP3kernel-livepatch-SLE15-SP3_Update_54before 5-150300.2.15-150300.2.1
SUSE:Linux Enterprise Live Patching 15 SP3kernel-livepatch-SLE15-SP3_Update_55before 5-150300.2.15-150300.2.1
SUSE:Linux Enterprise Live Patching 15 SP3kernel-livepatch-SLE15-SP3_Update_56before 3-150300.2.13-150300.2.1
SUSE:Linux Enterprise Live Patching 15 SP3kernel-livepatch-SLE15-SP3_Update_57before 3-150300.2.13-150300.2.1
SUSE:Linux Enterprise Live Patching 15 SP3kernel-livepatch-SLE15-SP3_Update_58before 2-150300.2.12-150300.2.1
SUSE:Linux Enterprise Live Patching 15 SP4kernel-livepatch-SLE15-SP4_Update_28before 16-150400.2.116-150400.2.1
SUSE:Linux Enterprise Live Patching 15 SP4kernel-livepatch-SLE15-SP4_Update_34before 10-150400.2.110-150400.2.1
SUSE:Linux Enterprise Live Patching 15 SP4kernel-livepatch-SLE15-SP4_Update_35before 9-150400.2.19-150400.2.1

+73

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    83Now
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    77This week
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Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux020ecb76812a0526f4130ab5aeb6dc7c773e7ab9Vendor (CNA)
Linux Linux647cef20e649c576dff271e018d5d15d998b629dVendor (CNA)
Linux Linux78285b53266d6d51fa4ff504a23df03852eba84eVendor (CNA)
Linux Linux79a955ea4a2e5ddf4a36328959de0de496419888Vendor (CNA)
Linux Linux7a9723ec27aff5674f1fd4934608937f1d650980Vendor (CNA)
Linux Linuxa56a6e8589a9b98d8171611fbcc1e45a15fd2455Vendor (CNA)
Linux Linuxb6a079c3b6f95378f26e2aeda520cb3176f7067bVendor (CNA)
Linux Linuxe40cb34b7f247fe2e366fd192700d1b4f38196caVendor (CNA)
debian:linux6.1.133-1 · Debian:12Package registry (OSV)
opensuse:kernel-azure6.4.0-150600.8.40.1 · openSUSE:Leap 15.6Package registry (OSV)
opensuse:kernel-source-azure6.4.0-150600.8.40.1 · openSUSE:Leap 15.6Package registry (OSV)
opensuse:kernel-syms-azure6.4.0-150600.8.40.1 · openSUSE:Leap 15.6Package registry (OSV)
suse:kernel-64kb6.4.0-150600.23.53.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP6Package registry (OSV)
suse:kernel-azure6.4.0-150600.8.40.1 · SUSE:Linux Enterprise Module for Public Cloud 15 SP6Package registry (OSV)
suse:kernel-default6.4.0-150600.23.53.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP6Package registry (OSV)
suse:kernel-default-base6.4.0-150600.23.53.1.150600.12.24.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP6Package registry (OSV)
suse:kernel-docs6.4.0-150600.23.53.1 · SUSE:Linux Enterprise Module for Development Tools 15 SP6Package registry (OSV)
suse:kernel-source6.4.0-150600.23.53.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP6Package registry (OSV)
suse:kernel-source-azure6.4.0-150600.8.40.1 · SUSE:Linux Enterprise Module for Public Cloud 15 SP6Package registry (OSV)
suse:kernel-syms-azure6.4.0-150600.8.40.1 · SUSE:Linux Enterprise Module for Public Cloud 15 SP6Package registry (OSV)
suse:kernel-zfcpdump6.4.0-150600.23.53.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP6Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
High
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

—

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Noroxi analysis

No Noroxi analysis for this record yet

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Change log

  1. Fix✗ → ✓

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References

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