CVE-2025-21702

Published Feb 18, 2025

Last updated a month ago

CVSS high 7.8

Overview

Description
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.
Source
416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD status
Modified
Products
linux_kernel

Risk scores

CVSS 3.1

Type
Primary
Base score
7
Impact score
5.9
Exploitability score
1
Vector string
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Severity
HIGH

Weaknesses

nvd@nist.gov
NVD-CWE-noinfo

Social media

Hype score
Not currently trending

  1. 🔒 URGENT: #openSUSE kernel patches for 3 critical CVEs (CVE-2025-37797, CVE-2025-37752, CVE-2025-21702) are live! DoS risks threaten unpatched systems—especially networks using HFSC/SFQ scheduling. 👉 https://t.co/JkPnR7DScY https://t.co/dKVwjDqDG6

    @Cezar_H_Linux

    5 Aug 2025

    38 Impressions

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  2. 🚨 Critical Linux Kernel RT flaws patched! CVE-2025-21702 allows RCE in #openSUSE/SLE systems. ⏩ Patch IMMEDIATELY. Read more: 👉 https://t.co/Svoo1RvcN0 https://t.co/jRu9T5dHm3

    @Cezar_H_Linux

    4 Aug 2025

    40 Impressions

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  3. 🚨 Critical #LinuxKernel Patches! SUSE Live Patch 38 (SLE 15 SP4 / openSUSE Leap 15.4) fixes 4 HIGH-sev vulns: ✅ CVE-2025-37797 (HFSC UAF). ✅ CVE-2024-53125 (BPF flaw). ✅ CVE-2025-21702 (pfifo). ✅ CVE-2025-37752 (SFQ). Read more:👉 https://t.co/9xiz3h2QSu https://t.c

    @Cezar_H_Linux

    4 Aug 2025

    46 Impressions

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  4. CVE-2025-21702 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 sc… https://t.co/HW8b4i0ju3

    @CVEnew

    18 Feb 2025

    236 Impressions

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Configurations

Related CVEs

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References

Sources include official advisories and independent security research.