CVE-2021-47245: netfilter: synproxy: Fix out of bounds when parsing TCP options
Vulnerability summary
CVE-2021-47245 is a high (CVSS 8.2) Out-of-bounds Read vulnerability in linux. EPSS estimates a 0.78% chance of exploitation in the next 30 days, higher than 56% of scored vulnerabilities.
Severe, CVSS 8.2 (CVE.org); no exploitation reported by the 5 checked sources; EPSS 1% (FIRST, 03-11-2026)
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 7 · Related 7Timeline
- 21-05-2024PublishedVulnerability first disclosed.
- 05-08-2026Last modifiedVulnerability information updated.
Description
In the Linux kernel, the following vulnerability has been resolved: netfilter: synproxy: Fix out of bounds when parsing TCP options The TCP option parser in synproxy (synproxy_parse_options) could read one byte out of bounds. When the length is 1, the execution flow gets into the loop, reads one byte of the opcode, and if the opcode is neither TCPOPT_EOL nor TCPOPT_NOP, it reads one more byte, which exceeds the length of 1. This fix is inspired by commit 9609dad263f8 ("ipv4: tcp_input: fix stack out of bounds when parsing TCP options."). v2 changes: Added an early return when length < 0 to avoid calling skb_header_pointer with negative length.
CVSS metrics
5 scores · 4 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated8.2HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
- OSV · DebianEcosystem advisory · calculated7.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:HDiffers
- NVDNIST7.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:HDiffers
EPSS trend
Probability
0.78%
Chance of exploitation in the next 30 days
Percentile
56%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.78% 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: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Ubuntu86 products
- linuxAll versions (No fix recorded) | < 4.4.0-268.302 | < 4.15.0-156.163 | < 5.4.0-81.91
- linux-allwinner-5.19All versions (No fix recorded)
- linux-aws< 4.4.0-1143.149 | < 4.4.0-1181.196 | < 4.15.0-1111.118 | < 5.4.0-1055.58
- linux-aws-5.0All versions (No fix recorded)
- linux-aws-5.11All versions (No fix recorded)
Linux2 products
- linux≥ 48b1de4c110a7afa4b85862f6c75af817db26fad, < e1eb98cfeafdd85537e7e3cefe93ca9bfbcc3ea8 | ≥ 48b1de4c110a7afa4b85862f6c75af817db26fad, < 576c1526b4d83c44ad7b673cb841f36cbc6cb6c4 | ≥ 48b1de4c110a7afa4b85862f6c75af817db26fad, < 674b5f0c6a4fc5d3abce877048290cea6091fcb1 | ≥ 48b1de4c110a7afa4b85862f6c75af817db26fad, < 7d9a9a1a88a3da574e019b4de756bc73337b3b0b | ≥ 48b1de4c110a7afa4b85862f6c75af817db26fad, < 6defc77d48eff74075b80ad5925061b2fc010d98 | ≥ 48b1de4c110a7afa4b85862f6c75af817db26fad, < 9cdf299ba4e153b5e56187648420de22c6216f02 | ≥ 48b1de4c110a7afa4b85862f6c75af817db26fad, < f648089337cb8ed40b2bb96e244f72b9d97dc96b | ≥ 48b1de4c110a7afa4b85862f6c75af817db26fad, < 5fc177ab759418c9537433e63301096e733fb915 | 3.12
- linux_kernel≥ 3.12, < 4.4.274 | ≥ 4.5, < 4.9.274 | ≥ 4.10, < 4.14.238 | ≥ 4.15, < 4.19.196 | ≥ 4.20, < 5.4.128 | ≥ 5.5, < 5.10.46 | ≥ 5.11, < 5.12.13 | 5.13:rc1 | 5.13:rc2 | 5.13:rc3 | 5.13:rc4 | 5.13:rc5 | 5.13:rc6
Debian1 product
- linux< 5.10.46-1
3 vendors · 89 products
