Local privilege escalation via stale tcindex allocation size
Published May 7, 2025 · Updated Aug 5, 2026
Out-of-bounds access in the Linux kernel's tcindex classifier allows local users to disclose or corrupt kernel memory. The tcindex_set_parms path allocates a resized perfect-hash array but retains the prior cp->alloc_hash value, so an attacker-controlled handle indexes beyond the new allocation. Access requires local netlink configuration privileges; unprivileged user namespaces can supply CAP_NET_ADMIN, and exploitation can crash the host or elevate privileges.
Summary
What happened
Out-of-bounds access in the Linux kernel's tcindex classifier allows local users to disclose or corrupt kernel memory. The tcindex_set_parms path allocates a resized perfect-hash array but retains the prior cp->alloc_hash value, so an attacker-controlled handle indexes beyond the new allocation. Access requires local netlink configuration privileges; unprivileged user namespaces can supply CAP_NET_ADMIN, and exploitation can crash the host or elevate privileges.
The record
- CVE
- CVE-2020-36791
- Published
- May 7, 2025
- Updated
- Aug 5, 2026
- Vendor
- The Linux Kernel Organization
- Product
- Linux
- Classifications
- CWE-125, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- May 7, 2025CVE publishedPublication date reported by the CVE source.
- Aug 5, 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=2c66ff8d08f81bcf8e8cb22e31e39c051b15336a <bd3ee8fb6371b45c71c9345cc359b94da2ddefa9
- Affected versionversion=4.14.171 <4.14.175
- Affected versionversion=4.19.103 <4.19.114
- Affected versionversion=4.4.214 <4.4.218
- Affected versionversion=478c4b2ffd44e5186c7e22ae7c38a86a5b9cfde5 <557d015ffb27b672e24e6ad141fd887783871dc2
- Affected versionversion=4.9.214 <4.9.218
- Affected versionversion=5.4.19 <5.4.29
- Affected versionversion=5.5.3 <5.5.14
- Affected versionversion=599be01ee567b61f4471ee8078870847d0a11e8e <0d1c3530e1bd38382edef72591b78e877e0edcd3
- Affected versionversion=6cb448ee493c8a514c9afa0c346f3f5b3227de85 <9f8b6c44be178c2498a00b270872a6e30e7c8266
- Affected versionversion=73c29d2f6f8ae731b1e09051b69ed3ba2319482b <d6cdc5bb19b595486fb2e6661e5138d73a57f454
- Affected versionversion=b974ac51f5834a729de252fc5c1c9de9efd79b45 <c4453d2833671e3a9f6bd52f0f581056c3736386
- Affected versionversion=dd8142a6fa5270783d415292ec8169f4ea2a5468 <d23faf32e577922b6da20bf3740625c1105381bf
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
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
- syzbot tcindex_set_parms slab-out-of-bounds reproducerproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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