CVE-2026-93405Public exploitNetwork attack vector

Stored XSS via unsanitized attachment conversion

Published Sep 24, 2026 · Updated Sep 24, 2026

Stored XSS in Mailspring before 1.17.0 allows remote attackers to execute script in the quick-preview renderer via a crafted attachment. The quick-preview code converts Markdown, DOCX, and XLSX content to HTML and assigns the unsanitized result to the preview document's innerHTML. Exploitation requires a recipient to open quick preview and is confined to that renderer; persistent code execution requires two separate flaws.

CVSS severity6.1
Medium
EPSS probability0.22%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in Mailspring before 1.17.0 allows remote attackers to execute script in the quick-preview renderer via a crafted attachment. The quick-preview code converts Markdown, DOCX, and XLSX content to HTML and assigns the unsanitized result to the preview document's innerHTML. Exploitation requires a recipient to open quick preview and is confined to that renderer; persistent code execution requires two separate flaws.

The record

CVE
CVE-2026-93405
Published
Sep 24, 2026
Updated
Sep 24, 2026
Vendor
Foundry 376, LLC
Product
Mailspring
Classifications
CWE-79, T1204.002, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 24, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.17.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Foundry 376, LLC · Mailspringversion=< 1.17.0

Published CVSS scores

6.1Foundry376/MailspringCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1204.002Malicious File
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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