CVE-2026-35539: Roundcube Webmail Insufficient HTML Attachment Sanitization Vulnerability

MODERATE
Advisory Identifier: GHSA-x4q5-8j5g-hpjc
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CVSS 6.1
CWE-79
Published
Advisory Summary

CVE-2026-35539 is a MODERATE (CVSS 6.1) insufficient html attachment sanitization vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Roundcube Webmail libraries in the Packagist ecosystem. The issue involves insufficient html attachment sanitization in preview mode. Remediation is available by upgrading affected packages to version 1.7-rc5.

CVE-2026-35539 at a Glance

CVE Identifier CVE-2026-35539
GHSA Identifier GHSA-x4q5-8j5g-hpjc
Severity MODERATE
CVSS v3.1 Base Score 6.1
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Roundcube Webmail
Package Ecosystem Packagist
Published Date
Last Updated

Security Impact

CVSS: 6.1

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction Required (UI:R)
Scope Changed (S:C)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-35539

To remediate this vulnerability, upgrade all affected Roundcube Webmail dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

roundcube/roundcubemail fixed: 1.7-rc5 
Upgrade roundcube/roundcubemail to 1.7-rc5
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for roundcube/roundcubemail

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-35539, inspect your project dependencies for Roundcube Webmail:

inspect dependencies for roundcube/roundcubemail

Analyze the terminal output to locate any version of Roundcube Webmail in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.7-rc5), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Roundcube Webmail, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

An issue was discovered in Roundcube Webmail before 1.5.14 and 1.6.14. XSS exists because of insufficient HTML attachment sanitization in preview mode. A victim must preview a text/html attachment.

CVE-2026-35539 Affected Roundcube Webmail Versions

1 component(s)
Fixed Versions:
1.7-rc5
Product / Package Ecosystem Affected Versions Fixed Version
roundcube/roundcubemail
 Packagist
≥ 1.7-beta
< 1.7-rc5
1.7-rc5

References

NVD — CVE-2026-35539 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-35539
Security Fix Commit FIX COMMIT
https://github.com/roundcube/roundcubemail/commit/10a6d1fa8acac85c727b0a6ae4a6642bfa27bea1
Security Fix Commit FIX COMMIT
https://github.com/roundcube/roundcubemail/commit/1b30edf5369668c92fe91dae3d52e477c808aa4f
Security Fix Commit FIX COMMIT
https://github.com/roundcube/roundcubemail/commit/d742954ccbcdee7020f8f2e7c49ce0fca5a0efab
Roundcube Webmail Source Repository REPOSITORY
https://github.com/roundcube/roundcubemail
Roundcube Webmail Release RELEASE
https://github.com/roundcube/roundcubemail/releases/tag/1.5.14
Roundcube Webmail Release RELEASE
https://github.com/roundcube/roundcubemail/releases/tag/1.6.14
Roundcube Webmail Release RELEASE
https://github.com/roundcube/roundcubemail/releases/tag/1.7-rc5
Roundcube Webmail Security Information SECURITY
https://roundcube.net/news/2026/03/18/security-updates-1.7-rc5-1.6.14-1.5.14

Frequently Asked Questions

What is CVE-2026-35539?
CVE-2026-35539 is a security vulnerability in Roundcube Webmail involving Insufficient HTML attachment sanitization in preview mode under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Roundcube Webmail versions are affected?
Affected versions include releases prior to 1.7-rc5 across affected packages: roundcube/roundcubemail.
What version fixes CVE-2026-35539?
Upgrading to 1.7-rc5 (or the latest patched release for your respective branch) resolves the vulnerability.
Is roundcube/roundcubemail affected?
Yes, roundcube/roundcubemail is affected in releases prior to 1.7-rc5. Upgrade your dependency to 1.7-rc5 or later.
What is the CVSS score of CVE-2026-35539?
CVE-2026-35539 has a CVSS v3.1 base score of 6.1 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
What CWE is associated with CVE-2026-35539?
CVE-2026-35539 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check Packagist dependencies for CVE-2026-35539?
Run the dependency tree command: 'inspect dependencies for roundcube/roundcubemail'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-x4q5-8j5g-hpjc",
  "modified" : "2026-04-04T06:50:55Z",
  "published" : "2026-04-03T06:31:32Z",
  "aliases" : [ "CVE-2026-35539" ],
  "summary" : "Roundcube Webmail: Insufficient HTML attachment sanitization in preview mode",
  "details" : "An issue was discovered in Roundcube Webmail before 1.5.14 and 1.6.14. XSS exists because of insufficient HTML attachment sanitization in preview mode. A victim must preview a text/html attachment.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "roundcube/roundcubemail"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.7-beta"
      }, {
        "fixed" : "1.7-rc5"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-35539"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/roundcube/roundcubemail/commit/10a6d1fa8acac85c727b0a6ae4a6642bfa27bea1"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/roundcube/roundcubemail/commit/1b30edf5369668c92fe91dae3d52e477c808aa4f"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/roundcube/roundcubemail/commit/d742954ccbcdee7020f8f2e7c49ce0fca5a0efab"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/roundcube/roundcubemail"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/roundcube/roundcubemail/releases/tag/1.5.14"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/roundcube/roundcubemail/releases/tag/1.6.14"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/roundcube/roundcubemail/releases/tag/1.7-rc5"
  }, {
    "type" : "WEB",
    "url" : "https://roundcube.net/news/2026/03/18/security-updates-1.7-rc5-1.6.14-1.5.14"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-04T06:50:55Z",
    "nvd_published_at" : "2026-04-03T05:16:21Z"
  }
}