CVE-2021-20177: linux linux_kernel Out-of-bounds Read
Vulnerability summary
CVE-2021-20177 is a medium (CVSS 4.4) Out-of-bounds Read vulnerability in linux linux_kernel. EPSS estimates a 0.28% chance of exploitation in the next 30 days, higher than 20.9% of scored vulnerabilities.
Not severe (CVSS 4.4, local access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 11 · Related 9Timeline
- 26-05-2021PublishedVulnerability first disclosed.
- 03-08-2024Last modifiedVulnerability information updated.
Description
A flaw was found in the Linux kernel's implementation of string matching within a packet. A privileged user (with root or CAP_NET_ADMIN) when inserting iptables rules could insert a rule which can panic the system. Kernel before kernel 5.5-rc1 is affected.
CVSS metrics
4 scores · 3 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated4.4MediumCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
- OSV · DebianEcosystem advisory · calculated4.4MediumCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
EPSS trend
Probability
0.28%
Chance of exploitation in the next 30 days
Percentile
21%
Versus all other CVEs
30-day change
Increase +0.01 pp
From 0.28% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Known conditions: local access, administrative account, no user interaction (CVSS vector). Other conditions: not stated in public data.
Ubuntu36 products
- linux< 5.4.0-66.74
- linux-aws< 5.4.0-1038.40
- linux-aws-5.0All versions (No fix recorded)
- linux-aws-5.3All versions (No fix recorded)
- linux-aws-5.4< 5.4.0-1038.40~18.04.1
Debian1 product
- linux< 5.5.13-1
Linux1 product
- linux_kernel≤ 5.4.9
3 vendors · 38 products
