lettre is a a mailer library for Rust. Starting in version 0.10.1 and prior to version 0.11.22, 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. Version 0.11.22 patches the issue.
CVE-2026-46428
CRITICALPre-NVD 9.19.1—Trending — 3 sources updated this weekElevated
EchelonGraph scoreMEDIUM confidence
This critical-severity CVE scores 9.1 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.2%, top 91% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
Triggered by: NVD CVSS baseline
Sources: epss, secondary
9.1
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
- High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 9.1Exploit: NoneExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 9.1
- EG Score
- 9.1(medium)
- EG Risk
- 57(Track*)EG Risk 57/100SSVC: Track*
EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).
How it’s computedSeverity91% × 45%Exploitation40% × 40%Automatability0% × 15%Action: Watch closely — could escalate to Attend. - EPSS
- 9.0%
- KEV
- Not listed
Published
July 20, 2026
Last Modified
July 21, 2026
Advisory Details (4)
Auto-updated Jul 20, 2026🔬 Proof of concept available. Patch available. Sources: github_commit, github_release, github.
generic
RUSTSEC-2026-0141: lettre: TLS hostname verification disabled when using Boring TLS backend › RustSec Advisory Database
https://rustsec.org/advisories/RUSTSEC-2026-0141.htmlgithub Patch Available🟡 PoC Available
TLS hostname verification disabled when using Boring TLS backend · Advisory · lettre/lettre · GitHub
https://github.com/lettre/lettre/security/advisories/GHSA-4pj9-g833-qx53github_release Patch Available
v0.11.22 - update now if you're using Boring TLS
Patch available: lettre/lettre v0.11.22
https://github.com/lettre/lettre/releases/tag/v0.11.22github_commit Patch Available
commit f5efffc88360 (lettre/lettre)
Patch available: lettre/lettre v0.11.22 (contains commit f5efffc88360)
https://github.com/lettre/lettre/commit/f5efffc88360dbdbfcef80f465e42d5bce68ca35Affected Packages
(1 across 1 ecosystem)
crates.io(1)
| Package | Vulnerable range | Fixed in | Dependents |
|---|---|---|---|
| lettre | — | 0.11.22 | — |
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 7× in last 7d / 7× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-07-23 03:17 UTCEG score recompute
- 2026-07-22 23:37 UTCEG score recompute
- 2026-07-22 14:08 UTCEPSS rescore
- 2026-07-21 15:24 UTCEPSS rescore
- 2026-07-20 16:37 UTCEG score recompute
- 2026-07-20 16:03 UTCEG score recompute
- 2026-07-20 16:02 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Same CWE
10 shownCWE-295
Frequently asked(5)
What is CVE-2026-46428?
CVE-2026-46428 is a critical vulnerability published on July 20, 2026. lettre is a a mailer library for Rust. Starting in version 0.10.1 and prior to version 0.11.22, 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…
When was CVE-2026-46428 disclosed?
CVE-2026-46428 was first published in the National Vulnerability Database on July 20, 2026, with the most recent update on July 21, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-46428 actively exploited?
CVE-2026-46428 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 9.0% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-46428?
CVE-2026-46428 has a CVSS v3 base score of 9.1 (NVD).
How do I remediate CVE-2026-46428?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-46428, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-46428
Is Your Infrastructure Affected by CVE-2026-46428?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.