Service interruption via unchecked flow-classifier shift
Published Jan 19, 2025 · Updated May 12, 2026
Improper input validation in the Linux kernel flow classifier allows local users to interrupt affected Linux and SIMATIC S7-1500 TM MFP systems. The cls_flow parser accepts TCA_FLOW_RSHIFT values larger than 31, then flow_classify right-shifts a 32-bit key by that unchecked count. Exploitation requires low-privileged local access and a traffic-control path that invokes cls_flow; the undefined operation occurs in kernel context.
Summary
What happened
Improper input validation in the Linux kernel flow classifier allows local users to interrupt affected Linux and SIMATIC S7-1500 TM MFP systems. The cls_flow parser accepts TCA_FLOW_RSHIFT values larger than 31, then flow_classify right-shifts a 32-bit key by that unchecked count. Exploitation requires low-privileged local access and a traffic-control path that invokes cls_flow; the undefined operation occurs in kernel context.
The record
- CVE
- CVE-2025-21653
- Published
- Jan 19, 2025
- Updated
- May 12, 2026
- Vendor
- Siemens
- Product
- SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
- Classifications
- CWE-20, T1499
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Jan 19, 2025CVE publishedPublication date reported by the CVE source.
- May 12, 2026Record updatedLatest update available in the CVE record.
Exploitability
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- Affected versionversion=0 <*
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Published CVSS scores
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Attacks
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Technologies
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