CVE-2026-24904: TrustTunnel has `client_random_prefix` rule bypass via fragmented or partial TLS ClientHello

Vulnerability summary

CVE-2026-24904 is a medium (CVSS 5.3) Improper Access Control vulnerability in adguard trusttunnel. EPSS estimates a 0.30% chance of exploitation in the next 30 days, higher than 22.6% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 29-01-2026
   PublishedVulnerability first disclosed.
2. 29-01-2026
   Last modifiedVulnerability information updated.

Description

TrustTunnel is an open-source VPN protocol with a rule bypass issue in versions prior to 0.9.115. In `tls_listener.rs`, `TlsListener::listen()` peeks 1024 bytes and calls `extract_client_random(...)`. If `parse_tls_plaintext` fails (for example, a fragmented/partial ClientHello split across TCP writes), `extract_client_random` returns `None`. In `rules.rs`, `RulesEngine::evaluate` only evaluates `client_random_prefix` when `client_random` is `Some(...)`. As a result, when extraction fails (`client_random == None`), any rule that relies on `client_random_prefix` matching is skipped and evaluation falls through to later rules. As an important semantics note: `client_random_prefix` is a match condition only. It does not mean "block non-matching prefixes" by itself. A rule with `client_random_prefix = ...` triggers its `action` only when the prefix matches (and the field is available to evaluate). Non-matches (or `None`) simply do not match that rule and continue to fall through. The vulnerability is fixed in version 0.9.115.

• CWE-284Improper Access ControlThe product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.