CVE-2026-63435

MEDIUMPre-NVD 5.35.3—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 74% 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
5.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.3Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Mail is an internet library for Ruby designed to handle email generation, parsing, and sending. Prior to 2.9.1, Mail::Utilities.q_value_decode and Mail::Utilities.b_value_decode used a single String#match and an overly greedy charset capture to decode only the first RFC 2047 encoded-word and mishandle surrounding or subsequent text. A crafted malformed encoded-word in an address display name or local part could cross ? delimiters and make decoded From, To, or Reply-To header values differ from the raw values inspected by a human reviewer or downstream parser, enabling apparent sender or recipient spoofing, phishing, or authorization-check bypass. This issue is fixed in version 2.9.1.

CVSS v3
5.3
EG Score
5.3(medium)
EG Risk
39(Track)
EG Risk 39/100SSVC: 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 computed
Severity53% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
26%
KEV
Not listed

Published

September 1, 2026

Last Modified

September 9, 2026

Advisory Details (4)

Auto-updated Sep 1, 2026
Patch available. Sources: github, github_pr, github_commit, github_release.
github_release Patch Available

2.9.1

Patch available: mikel/mail 2.9.1

https://github.com/mikel/mail/releases/tag/2.9.1
github_commit Patch Available

commit f9d59c2e447a (mikel/mail)

Patch available: mikel/mail 2.9.1 (contains commit f9d59c2e447a)

https://github.com/mikel/mail/commit/f9d59c2e447af42e2c3dec5a56b1bb25c7292859
github_pr Patch Available

Improve decoding of Q- and B-encoded strings

Patch available: mikel/mail 2.9.1 (PR #1664 merged 2026-07-01)

https://github.com/mikel/mail/pull/1664
github Patch Available

Email address spoofing via malformed RFC 2047 encoded-words in mail · Advisory · mikel/mail · GitHub

https://github.com/mikel/mail/security/advisories/GHSA-mvxr-6m87-mv2q

Vendor Advisories for CVE-2026-63435(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(4 across 4 ecosystems)
Debian:12(1)
PackageVulnerable rangeFixed inDependents
ruby-mail2.7.1+dfsg1-2, 2.8.1+dfsg1-1, 2.8.1+dfsg1-2, 2.9.0+dfsg1-1, 2.9.1-1——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
ruby-mail2.8.1+dfsg1-2, 2.9.0+dfsg1-1, 2.9.1-1——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
ruby-mail2.8.1+dfsg1-2, 2.9.0+dfsg1-12.9.1-1—
RubyGems(1)
PackageVulnerable rangeFixed inDependents
mail1.0.0 ... 2.9.0.beta2 (96 versions)2.9.1—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 10× in last 7d / 31× 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.

  1. 2026-09-19 00:57 UTCEG score recompute
  2. 2026-09-18 19:28 UTCEPSS rescore
  3. 2026-09-18 03:01 UTCEG score recompute
  4. 2026-09-17 05:05 UTCEG score recompute
  5. 2026-09-16 14:08 UTCEPSS rescore
  6. 2026-09-16 07:09 UTCEG score recompute
  7. 2026-09-16 05:15 UTCEPSS rescore
  8. 2026-09-15 09:13 UTCEG score recompute
  9. 2026-09-14 11:17 UTCEG score recompute
  10. 2026-09-12 15:27 UTCEG score recompute
  11. 2026-09-11 17:27 UTCEG score recompute
  12. 2026-09-11 14:53 UTCEPSS rescore
  13. 2026-09-11 09:37 UTCEPSS rescore
  14. 2026-09-10 19:06 UTCEG score recompute
  15. 2026-09-09 02:20 UTCEG score recompute
  16. 2026-09-08 22:01 UTCEPSS rescore
  17. 2026-09-08 04:18 UTCEG score recompute
  18. 2026-09-07 16:01 UTCEPSS rescore
  19. 2026-09-07 06:22 UTCEG score recompute
  20. 2026-09-06 13:47 UTCEPSS rescore
  21. 2026-09-06 08:23 UTCEG score recompute
  22. 2026-09-05 15:31 UTCEPSS rescore
  23. 2026-09-05 10:27 UTCEG score recompute
  24. 2026-09-04 12:32 UTCEG score recompute
  25. 2026-09-04 05:07 UTCEPSS rescore
Show 6 more
  1. 2026-09-02 16:38 UTCEG score recompute
  2. 2026-09-02 15:53 UTCEG score recompute
  3. 2026-09-02 14:12 UTCEPSS rescore
  4. 2026-09-01 21:27 UTCEG score recompute
  5. 2026-09-01 20:23 UTCEG score recompute
  6. 2026-09-01 20:22 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-63435?
CVE-2026-63435 is a medium vulnerability published on September 1, 2026. Mail is an internet library for Ruby designed to handle email generation, parsing, and sending. Prior to 2.9.1, Mail::Utilities.qvaluedecode and Mail::Utilities.bvaluedecode used a single String#match and an overly greedy charset capture to decode only the first RFC 2047 encoded-word and mishandle…
When was CVE-2026-63435 disclosed?
CVE-2026-63435 was first published in the National Vulnerability Database on September 1, 2026, with the most recent update on September 9, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-63435 actively exploited?
CVE-2026-63435 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 73.8% of all scored CVEs.
What is the CVSS score of CVE-2026-63435?
CVE-2026-63435 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2026-63435?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-63435, 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

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