Machine-written summary
Summary written by Claude Haiku from the source advisory. Not reviewed by a person.
The lettre crate versions 0.10.1 up to but not including 0.11.22 are affected when built with the boring-tls feature, where an inverted boolean silently disables TLS hostname verification under the default strict configuration. An on-path attacker holding any certificate that chains to a trusted root for any domain could intercept SMTP submission, including login credentials and message contents. The native-tls and rustls backends are not affected. Upgrade to lettre 0.11.22 or later.
Not analysed yet
We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.
Severity and exploitation
| Score | Rating | CVSS | Vector | Source |
|---|---|---|---|---|
| 9.1 | Critical | 4.0 | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N | CNA (GitHub_M) |
- CISA KEV Not listed.
- EPSS 0.0032, the 25th percentile, on 12 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.
Timeline
- 31 Oct 2026, 14:24 UTC First seen by agentprime
- 31 Oct 2026, 14:24 UTC Confirmed by OSV