GHSA-mvxr-6m87-mv2q is a medium-severity (CVSS 5.3) CWE-436 vulnerability in mail. O3 Security confirms whether GHSA-mvxr-6m87-mv2q is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Mail: Email address spoofing via malformed RFC 2047 encoded-words
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-mvxr-6m87-mv2q.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-mvxr-6m87-mv2q plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 367,633 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
mailReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Mail::Utilities.q_value_decode and Mail::Utilities.b_value_decode decoded only the first RFC 2047 encoded-word in a string and used an overly greedy pattern to match the charset token. A crafted, malformed encoded-word embedded in an address display name or local part could cause the decoded output to differ from what a human reviewer or downstream parser would expect, allowing an attacker to spoof the apparent sender/recipient address.
Details
Both decoders used a single String#match against a pattern such as /=?(.+)??[Qq]?(.*)?=/m. Two problems:
- Single match, dropped remainder. Only the first =?charset?Q?...?= (or ?B?) word was decoded. Any additional encoded-words or surrounding text were not handled consistently, so the decoded result could silently omit or alter parts of the input.
- Greedy charset capture. (.+)? is greedy and matches across ? delimiters, so a malformed word could span more of the string than a strict RFC 2047 parse would, changing the boundary between "encoded" and "literal" text.
Impact
Applications using mail to parse and display or authorize based on decoded header values (From, To, Reply-To, etc.) may present or act on an address different from the one a validator inspecting the raw header would see. Primary risk is spoofing / phishing and authorization-check bypass. No RCE.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | mail | all versions | 2.9.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mail. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update mail to 2.9.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mvxr-6m87-mv2q is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-mvxr-6m87-mv2q is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-mvxr-6m87-mv2q. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-mvxr-6m87-mv2q in your dependencies?
O3 detects GHSA-mvxr-6m87-mv2q across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.