Local panic via unchecked blockcast recursion
Published Jul 19, 2026 · Updated Jul 19, 2026
Stack overflow in Linux Kernel 6.19 allows local users to trigger a kernel panic through recursive traffic-control blockcasts. In tcf_mirred_act(), the blockcast branch returned through tcf_blockcast() before incrementing sched_mirred_nest, so mirrored packets could recurse between shared egress blocks without reaching MIRRED_NEST_LIMIT. An unprivileged local user can create user and network namespaces, gain CAP_NET_ADMIN in the new network namespace, install the necessary mirred blockcast rules, and interrupt the host.
Summary
What happened
Stack overflow in Linux Kernel 6.19 allows local users to trigger a kernel panic through recursive traffic-control blockcasts. In tcf_mirred_act(), the blockcast branch returned through tcf_blockcast() before incrementing sched_mirred_nest, so mirrored packets could recurse between shared egress blocks without reaching MIRRED_NEST_LIMIT. An unprivileged local user can create user and network namespaces, gain CAP_NET_ADMIN in the new network namespace, install the necessary mirred blockcast rules, and interrupt the host.
The record
- CVE
- CVE-2026-63981
- Published
- Jul 19, 2026
- Updated
- Jul 19, 2026
- Vendor
- The Linux Kernel Organization
- Product
- Linux Kernel
- Classifications
- T1499
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Jul 19, 2026CVE publishedPublication date reported by the CVE source.
- Jul 19, 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?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=6.19
- Affected versionversion=906736728cea480a85803c67fafb1b0e78491922 <25fc9352590f5ef21ebf290432bd768b336693bc
- Affected versionversion=fe946a751d9b52b7c45ca34899723b314b79b249 <34457de389fb64a01fdcc71177dfebe65fd2d362
- Affected versionversion=fe946a751d9b52b7c45ca34899723b314b79b249 <a005fa5d7502eefec7ee6e1c01adadc06de2f9ad
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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