What’s Vulnerable › Vulnerabilities

CVE-2020-36791: net_sched: keep alloc_hash updated after hash allocation

• Severity: high (CVSS 7.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-05-07 · updated 2026-08-04
• Weakness: CWE-125

Description

In the Linux kernel, the following vulnerability has been resolved: net_sched: keep alloc_hash updated after hash allocation In commit 599be01ee567 ("net_sched: fix an OOB access in cls_tcindex") I moved cp->hash calculation before the first tcindex_alloc_perfect_hash(), but cp->alloc_hash is left untouched. This difference could lead to another out of bound access. cp->alloc_hash should always be the size allocated, we should update it after this tcindex_alloc_perfect_hash().

Affected products

• Linux kernel: from 4.4.214 before 4.4.218; from 4.9.214 before 4.9.218; from 4.14.171 before 4.14.175; from 4.19.103 before 4.19.114; from 5.4.19 before 5.4.29; from 5.5.3 before 5.5.14 — fixed in 4.14.175, 4.19.114, 4.4.218, 4.9.218, 5.4.29, 5.5.14

How to fix

Upgrade to a fixed version: Linux kernel 4.14.175, 4.19.114, 4.4.218, 4.9.218. Check the vendor advisory for mitigations.

References

• https://blog.cdthoughts.ch/2021/03/16/syzbot-bug.html
• https://git.kernel.org/stable/c/0d1c3530e1bd38382edef72591b78e877e0edcd3
• https://git.kernel.org/stable/c/557d015ffb27b672e24e6ad141fd887783871dc2
• https://git.kernel.org/stable/c/9f8b6c44be178c2498a00b270872a6e30e7c8266
• https://git.kernel.org/stable/c/bd3ee8fb6371b45c71c9345cc359b94da2ddefa9
• https://git.kernel.org/stable/c/c4453d2833671e3a9f6bd52f0f581056c3736386
• https://git.kernel.org/stable/c/d23faf32e577922b6da20bf3740625c1105381bf
• https://git.kernel.org/stable/c/d6cdc5bb19b595486fb2e6661e5138d73a57f454
• https://syzkaller.appspot.com/bug?id=ea260693da894e7b078d18fca2c9c0a19b457534

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