GO-2021-0241 BIT-golang-2021-33197 CVE-2021-33197

Attacker can drop certain headers in net/http/httputil

Not rated yet Go

Severity: Not rated yet; No source has published a CVSS score yet
Exploit chance (EPSS): 2.26%; Chance of exploitation in the next 30 days. Higher than 82.98% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: —; Not classified
Fix: 1.16.5; Upgrade stdlib to this version or later

Description

ReverseProxy can be made to forward certain hop-by-hop headers, including Connection. If the target of the ReverseProxy is itself a reverse proxy, this lets an attacker drop arbitrary headers, including those set by the ReverseProxy.Director.

Affected versions

Go

Package	Vulnerable	Fixed in
stdlib	`< 1.15.13` `>= 1.16.0-0, < 1.16.5`	`1.15.13` `1.16.5`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

stdlib Go → `1.16.5`

go

go get stdlib@v1.16.5 && go mod tidy

References

Fixes and patches

Issue reports

go.dev/issue/46313

Timeline

Feb 17, 2022 Published
May 20, 2024 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-4374-p667-p6c8 HTTP/2 rapid reset can cause excessive work in net/http	High Known exploited	Also affects stdlib
CVE-2020-0601 Certificate validation bypass on Windows in crypto/x509	High Known exploited	Also affects stdlib
RUSTSEC-2026-0382 Distrust compromised intermediate certificates in crypto/x509	Medium	Also affects stdlib
GO-2026-6613 HTTP/1 server connection desynchronization after 2xx CONNECT response in net/http	High	Also affects stdlib
GO-2026-6609 Lack of limit on size of parsed Range headers in net/http	High	Also affects stdlib
GO-2026-6608 Memory limit bypass when parsing MIME headers in net/textproto, mime/multipart	High	Also affects stdlib
GO-2026-6607 Reject malformed ECH outer extension references in crypto/tls	High	Also affects stdlib
GO-2026-6604 Root.Mkdir(All) can follow junctions out of the root on Windows in os	Critical	Also affects stdlib

Credits: Asta Olofsson, Mattias Grenfeldt (https://grenfeldt.dev)

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