Vulnerability in lettre (CVE-2026-46428)
Summary
Vulnerability in lettre (CVE-2026-46428). Risk of unauthorized operations or information disclosure. Exploitable via rustls. Mitigation: upgrade to 0.11.22 or later.
Original description
The description as published by the source.
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.
The bug was introduced in v0.10.1 and persists through v0.11.21 (latest).
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-46428 has been found in lettre.
Attackers can target a specific entry point like rustls over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade lettre to 0.11.22 or later.
If unsure, ask your IT team or search "lettre CVE-2026-46428" on the vendor's site.
CVE-2026-46428 (lettre) — CWE-295
Attack surface: rustls
Patched: 0.11.22 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-295) exists in lettre. Attackers reach the vulnerable code path via rustls.
Check the vendor advisory for the affected versions of lettre. Attack surface: rustls.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 0.11.22.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'lettre' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'lettre' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
lettreを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade lettre to 0.11.22ステージング環境で 0.11.22 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory github.com
- advisory rustsec.org
- advisory nvd.nist.gov
- package github.com
- package crates.io
- web github.com
- web github.com
- web github.com