vulnerability / NVI-00015261 / Revision 1
lettre has TLS hostname verification disabled when using Boring TLS backend
GitHub lists this reviewed advisory for lettre. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
lettre
source listed>= 0.10.1, < 0.11.22
### Summary An inverted-boolean bug in lettre's `boring-tls` integration silently disables TLS hostname verification for callers using the default (strict) configuration. An on-path attacker presenting any chain-valid certificate for any domain can intercept SMTP submission, including PLAIN/LOGIN credentials and message contents, against any lettre user built with the `boring-tls` feature. Other TLS backends (`native-tls`, `rustls`) are unaffected. ### Details boring's `SslConnectorBuilder::set_verify_hostname(bool)` / `verify_hostname(bool)` API takes a *verify* flag — `true` means enforce hostname verification, `false` means skip it. (Boring docs: https://docs.rs/boring/latest/boring/ssl/struct.ConnectConfiguration.html#method.set_verify_hostname) lettre's `TlsParametersBuilder` exposes the opposite-named flag `accept_invalid_hostnames: bool` — `true` means *accept invalid* (skip verification), `false` means verify. lettre passes this flag directly to boring at both TLS-upgrade sites, inverting the semantics: src/transport/smtp/client/net.rs:202 (sync) .verify_hostname(*accept_invalid_hostnames) src/transport/smtp/client/async_net.rs:377 (async) config.set_verify_hostnam
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
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04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
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- GHSA-4pj9-g833-qx53 ↗
GitHub Advisory Database · vendor advisory
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Public revision history
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- Revision 1 ·
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