GHSA-pmc3-p9hx-jq96
First published: Wed Apr 23 2025(Updated: )
### Description Before version 1.7.0, utls did not implement the TLS 1.3 downgrade protection mechanism specified in RFC 8446 Section 4.1.3 when using a utls ClientHello spec. This allowed an active network adversary to downgrade TLS 1.3 connections initiated by a utls client to a lower TLS version (e.g., TLS 1.2) by modifying the ClientHello message to exclude the SupportedVersions extension, causing the server to respond with a TLS 1.2 ServerHello (along with a downgrade canary in the ServerHello random field). Because utls did not check the downgrade canary in the ServerHello random field, clients would accept the downgraded connection without detecting the attack. This attack could also be used by an active network attacker to fingerprint utls connections. ### Fix Commit or Pull Request refraction-networking/utls#337, specifically refraction-networking/utls@f8892761e2a4d29054264651d3a86fda83bc83f9 ### References - https://github.com/refraction-networking/utls/issues/181
| Affected Software | Affected Version | How to fix |
|---|---|---|
| go/github.com/refraction-networking/utls | <1.7.0 | 1.7.0 |
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Reference Links
- https://github.com/refraction-networking/utls/security/advisories/GHSA-pmc3-p9hx-jq96
- https://github.com/refraction-networking/utls/issues/181
- https://github.com/refraction-networking/utls/pull/337
- https://github.com/refraction-networking/utls/commit/f8892761e2a4d29054264651d3a86fda83bc83f9
- https://github.com/advisories/GHSA-pmc3-p9hx-jq96 (Advisory)
Frequently Asked Questions
What is the severity of GHSA-pmc3-p9hx-jq96?
GHSA-pmc3-p9hx-jq96 is a high severity vulnerability due to the lack of TLS 1.3 downgrade protection.
How do I fix GHSA-pmc3-p9hx-jq96?
To fix GHSA-pmc3-p9hx-jq96, upgrade the utls package to version 1.7.0 or later.
What does GHSA-pmc3-p9hx-jq96 affect?
GHSA-pmc3-p9hx-jq96 affects versions of the utls library prior to 1.7.0.
What is the impact of GHSA-pmc3-p9hx-jq96?
The impact of GHSA-pmc3-p9hx-jq96 allows an active adversary to downgrade TLS 1.3 connections to lower versions, compromising security.
Can GHSA-pmc3-p9hx-jq96 be exploited?
Yes, GHSA-pmc3-p9hx-jq96 can be exploited by active network attackers to downgrade secure TLS connections.
- collector/github-advisory-latest
- source/GitHub
- alias/GHSA-pmc3-p9hx-jq96
- agent/software-canonical-lookup
- agent/weakness
- agent/references
- agent/last-modified-date
- agent/source
- agent/severity
- agent/softwarecombine
- agent/type
- agent/description
- agent/first-publish-date
- agent/tags
- agent/event
- package-manager/go