CVE-2026-35542: Roundcube Bypass Of Remote Image Blocking Vulnerability

MODERATE
Advisory Identifier: GHSA-5hf6-crg4-fg59
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CVSS 5.3
CWE-669
Published
Advisory Summary

CVE-2026-35542 is a MODERATE (CVSS 5.3) bypass of remote image blocking vulnerability (CWE-669: Incorrect Resource Transfer Between Spheres) affecting Roundcube libraries in the Packagist ecosystem. The issue involves bypass of remote image blocking via crafted body background attribute. Remediation is available by upgrading affected packages to version 1.7-rc5.

CVE-2026-35542 at a Glance

CVE Identifier CVE-2026-35542
GHSA Identifier GHSA-5hf6-crg4-fg59
Severity MODERATE
CVSS v3.1 Base Score 5.3
CWE Classification CWE-669: Incorrect Resource Transfer Between Spheres
Affected Product Roundcube
Package Ecosystem Packagist
Published Date
Last Updated

Security Impact

CVSS: 5.3

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:N/S:U/C:L/I:N/A:N).

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

How to Fix CVE-2026-35542

To remediate this vulnerability, upgrade all affected Roundcube 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-2026-35542, inspect your project dependencies for Roundcube:

inspect dependencies for roundcube/roundcubemail

Analyze the terminal output to locate any version of Roundcube 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-669: Incorrect Resource Transfer Between Spheres, where the product does not properly transfer a resource/behavior to another sphere, or improperly imports a resource/behavior from another sphere, in a manner that provides unintended control over that resource. In Roundcube, 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. The remote image blocking feature can be bypassed via a crafted background attribute of a BODY element in an e-mail message. This may lead to information disclosure or access-control bypass.

CVE-2026-35542 Affected Roundcube 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-2026-35542 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-35542
Security Fix Commit FIX COMMIT
https://github.com/roundcube/roundcubemail/commit/e052328e3dc75f13adc2e314eaa4096ac21084ad
Security Fix Commit FIX COMMIT
https://github.com/roundcube/roundcubemail/commit/fd0e98178db5c73eaa93d005b561874923f9b0f0
Security Fix Commit FIX COMMIT
https://github.com/roundcube/roundcubemail/commit/fde14d01adc9f37893cd82b635883e516ed453f8
Roundcube Source Repository REPOSITORY
https://github.com/roundcube/roundcubemail
Roundcube Release RELEASE
https://github.com/roundcube/roundcubemail/releases/tag/1.5.14
Roundcube Release RELEASE
https://github.com/roundcube/roundcubemail/releases/tag/1.6.14
Roundcube Release RELEASE
https://github.com/roundcube/roundcubemail/releases/tag/1.7-rc5
Roundcube 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-2026-35542?
CVE-2026-35542 is a security vulnerability in Roundcube involving Bypass of remote image blocking via crafted BODY background attribute under CWE-669: Incorrect Resource Transfer Between Spheres.
Which Roundcube versions are affected?
Affected versions include releases prior to 1.7-rc5 across affected packages: roundcube/roundcubemail.
What version fixes CVE-2026-35542?
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-2026-35542?
CVE-2026-35542 has a CVSS v3.1 base score of 5.3 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N.
What CWE is associated with CVE-2026-35542?
CVE-2026-35542 is classified under CWE-669: Incorrect Resource Transfer Between Spheres (The product does not properly transfer a resource/behavior to another sphere, or improperly imports a resource/behavior from another sphere, in a manner that provides unintended control over that resource.).
How can I check Packagist dependencies for CVE-2026-35542?
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-5hf6-crg4-fg59",
  "modified" : "2026-04-04T06:55:40Z",
  "published" : "2026-04-03T06:31:32Z",
  "aliases" : [ "CVE-2026-35542" ],
  "summary" : "Roundcube: Bypass of remote image blocking via crafted BODY background attribute",
  "details" : "An issue was discovered in Roundcube Webmail before 1.5.14 and 1.6.14. The remote image blocking feature can be bypassed via a crafted background attribute of a BODY element in an e-mail message. This may lead to information disclosure or access-control bypass.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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-2026-35542"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/roundcube/roundcubemail/commit/e052328e3dc75f13adc2e314eaa4096ac21084ad"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/roundcube/roundcubemail/commit/fd0e98178db5c73eaa93d005b561874923f9b0f0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/roundcube/roundcubemail/commit/fde14d01adc9f37893cd82b635883e516ed453f8"
  }, {
    "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-669" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-04T06:55:40Z",
    "nvd_published_at" : "2026-04-03T05:16:22Z"
  }
}