Local privilege escalation via qdisc accounting mismatch
Published Feb 18, 2025 · Updated Sep 8, 2026
Improper queue accounting in the Linux kernel allows local users to gain kernel privileges through crafted parent-child qdiscs. The pfifo_tail_enqueue function enqueues a packet when sch->limit is zero, increments the child queue length, and returns NET_XMIT_CN without the parent incrementing its length. Exploitation requires local low-privileged access and a graft-capable parent qdisc, producing an accounting mismatch that enables user-to-kernel escalation.
Summary
What happened
Improper queue accounting in the Linux kernel allows local users to gain kernel privileges through crafted parent-child qdiscs. The pfifo_tail_enqueue function enqueues a packet when sch->limit is zero, increments the child queue length, and returns NET_XMIT_CN without the parent incrementing its length. Exploitation requires local low-privileged access and a graft-capable parent qdisc, producing an accounting mismatch that enables user-to-kernel escalation.
The record
- CVE
- CVE-2025-21702
- Published
- Feb 18, 2025
- Updated
- Sep 8, 2026
- Vendor
- Siemens
- Product
- SIPLUS S7-1500 CPU 1518-4 PN/DP MFP
- Classifications
- CWE-787, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Feb 18, 2025CVE publishedPublication date reported by the CVE source.
- Sep 8, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=V3.1.5 <*
- Affected versionversion=V3.1.6 <*
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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