GO-2021-0239 BIT-golang-2021-33195 CVE-2021-33195

Improper sanitization when resolving values from DNS in net

Not rated yet Go

Severity: Not rated yet; No source has published a CVSS score yet
Exploit chance (EPSS): 3.20%; Chance of exploitation in the next 30 days. Higher than 88.15% 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

The LookupCNAME, LookupSRV, LookupMX, LookupNS, and LookupAddr functions and their respective methods on the Resolver type may return arbitrary values retrieved from DNS which do not follow the established RFC 1035 rules for domain names. If these names are used without further sanitization, for instance unsafely included in HTML, they may allow for injection of unexpected content. Note that LookupTXT may still return arbitrary values that could require sanitization before further use.

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/46241

Timeline

Feb 17, 2022 Published
May 20, 2024 Last updated by the source
Nov 1, 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: Haya Shulman from Fraunhofer SIT, Philipp Jeitner

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