CVE-2026-35537: Roundcube Webmail Unsafe Deserialization Vulnerability

LOW
Advisory Identifier: GHSA-rxj3-rrwm-pj4r
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CVSS 3.7
CWE-502
Published
Advisory Summary

CVE-2026-35537 is a LOW (CVSS 3.7) unsafe deserialization vulnerability (CWE-502: Deserialization of Untrusted Data) affecting Roundcube Webmail libraries in the Packagist ecosystem. The issue involves unsafe deserialization in the redis/memcache session handler. Remediation is available by upgrading affected packages to version 1.7-rc5.

CVE-2026-35537 at a Glance

CVE Identifier CVE-2026-35537
GHSA Identifier GHSA-rxj3-rrwm-pj4r
Severity LOW
CVSS v3.1 Base Score 3.7
CWE Classification CWE-502: Deserialization of Untrusted Data
Affected Product Roundcube Webmail
Package Ecosystem Packagist
Published Date
Last Updated

Security Impact

CVSS: 3.7

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

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

How to Fix CVE-2026-35537

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-2026-35537, 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-502: Deserialization of Untrusted Data, where the product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid. 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. Unsafe deserialization in the redis/memcache session handler may lead to arbitrary file write operations by unauthenticated attackers via crafted session data.

CVE-2026-35537 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-2026-35537 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-35537
Security Fix Commit FIX COMMIT
https://github.com/roundcube/roundcubemail/commit/618c5428edc69fb088e7ac6c89e506dd39df3
Security Fix Commit FIX COMMIT
https://github.com/roundcube/roundcubemail/commit/6d586cfa4d8a31f7957f7a445aaedd52592a0e74
Security Fix Commit FIX COMMIT
https://github.com/roundcube/roundcubemail/commit/a4ead994d2f0ea92e4a1603196a197e0d5df1620
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
Roundcube Webmail Security Information SECURITY
http://www.openwall.com/lists/oss-security/2026/04/11/6

Frequently Asked Questions

What is CVE-2026-35537?
CVE-2026-35537 is a security vulnerability in Roundcube Webmail involving Unsafe deserialization in the redis/memcache session handler under CWE-502: Deserialization of Untrusted Data.
Which Roundcube Webmail versions are affected?
Affected versions include releases prior to 1.7-rc5 across affected packages: roundcube/roundcubemail.
What version fixes CVE-2026-35537?
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-2026-35537?
CVE-2026-35537 has a CVSS v3.1 base score of 3.7 (LOW) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N.
What CWE is associated with CVE-2026-35537?
CVE-2026-35537 is classified under CWE-502: Deserialization of Untrusted Data (The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.).
How can I check Packagist dependencies for CVE-2026-35537?
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-rxj3-rrwm-pj4r",
  "modified" : "2026-04-14T21:55:54Z",
  "published" : "2026-04-03T06:31:32Z",
  "aliases" : [ "CVE-2026-35537" ],
  "summary" : "Roundcube Webmail: Unsafe deserialization in the redis/memcache session handler",
  "details" : "An issue was discovered in Roundcube Webmail before 1.5.14 and 1.6.14. Unsafe deserialization in the redis/memcache session handler may lead to arbitrary file write operations by unauthenticated attackers via crafted session data.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/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-2026-35537"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/roundcube/roundcubemail/commit/618c5428edc69fb088e7ac6c89e506dd39df3"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/roundcube/roundcubemail/commit/6d586cfa4d8a31f7957f7a445aaedd52592a0e74"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/roundcube/roundcubemail/commit/a4ead994d2f0ea92e4a1603196a197e0d5df1620"
  }, {
    "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"
  }, {
    "type" : "WEB",
    "url" : "http://www.openwall.com/lists/oss-security/2026/04/11/6"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-502" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-04T06:50:14Z",
    "nvd_published_at" : "2026-04-03T04:17:10Z"
  }
}