What’s Vulnerable › Vulnerabilities

CVE-2026-93405: Mailspring: Stored XSS in attachment quick preview (unsanitized Markdown/DOCX/XLSX conversion)

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-24 · updated 2026-09-30
• Weakness: CWE-79

Description

Mailspring is a fast, cross-platform, open-source email client. Prior to 1.17.0, attachment quick preview converts Markdown, DOCX, and XLSX attachments with Snarkdown, Mammoth, and SheetJS and inserts the resulting HTML into the preview document through innerHTML without sanitization. A remote sender can craft a supported attachment whose converted HTML executes script when a recipient opens quick preview. The preview renderer has no direct Node or Electron access, but injected script can reach the IPC surface exposed to the quick-preview renderer. This issue alone provides script execution in the preview renderer; separate path-traversal and renderer-controlled file-write vulnerabilities are required for the documented persistent code-execution chain. This issue is fixed in version 1.17.0.

Affected products

• Foundry376 Mailspring: before 1.17.0

References

• https://github.com/Foundry376/Mailspring/commit/5728388199666ec0a9a58f693c89c25b948a9b6c
• https://github.com/Foundry376/Mailspring/pull/2523
• https://github.com/Foundry376/Mailspring/releases/tag/1.17.0
• https://github.com/Foundry376/Mailspring/security/advisories/GHSA-px2g-jhg5-c6gh

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