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CWE-330Weakness · CWE-330

CVE-2026-42155

CRITICAL · 9.3 CVSS v4.0 Published 2026-05-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Magento Long Term Support (LTS) is an unofficial, community-driven project provides an alternative to the Magento Community Edition e-commerce platform with a high level of backward compatibility. Prior to 20.18.0, the XML-RPC / SOAP API session ID is generated using an outdated, time-based construction rather than a Cryptographically Secure Pseudo-Random Number Generator (CSPRNG). All inputs to the MD5 hash are time-derived and non-secure. Because the resulting digest relies entirely on the timestamp and the PHP internal LCG state, the effective entropy is severely constrained. This violates the OWASP ASVS v4 requirement of ≥ 64 bits of entropy (V3.2.2) and NIST SP 800-63B standards. By narrowing the LCG window (via server state leaks or general predictability) and leveraging the lack of API rate-limiting, an attacker can generate a localized pool of candidate MD5 hashes and execute a high-speed online brute-force attack to hijack active API sessions. This vulnerability is fixed in 20.18.0.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Magento LTS prior to 20.18.0 uses a time-based, non-CSPRNG construction for XML-RPC/SOAP API session ID generation. The MD5 hash relies solely on timestamp and PHP LCG state, providing severely constrained entropy (well below the 64-bit OWASP requirement). Attackers can narrow the LCG window and perform high-speed online brute-force to hijack active API sessions.

MitigationUpgrade to Magento LTS 20.18.0 or later which implements CSPRNG for session ID generation. Consider invalidating all existing API sessions and implementing API rate-limiting as defense-in-depth.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Determine installed Magento LTS version
    Check the composer.json file in the Magento root directory for the 'version' field, or run 'php bin/magento --version' from the command line
    Affected if The version is below 20.18.0 (for example, 20.17.x, 20.16.x, or earlier LTS releases)
  2. Confirm XML-RPC/SOAP API module is enabled
    Run 'php bin/magento module:status Magento_WebapiSoap' or inspect the app/etc/config.php file for 'Magento_WebapiSoap' => 1
    Affected if The XML-RPC/SOAP API module is listed as enabled (value of 1) in configuration
  3. Verify session ID generation method
    Inspect the session ID generation code in vendor/magento/framework/Session/SidResolver.php or similar session handling files for MD5-based timestamp construction
    Affected if Session IDs are generated using MD5 hashing of timestamps or PHP's LCG state rather than a cryptographically secure random number generator
  4. Check API endpoint accessibility
    Attempt a test request to the XML-RPC endpoint at /soap.php?wsdl&services=... or verify the endpoint responds in the web server access logs
    Affected if The XML-RPC/SOAP API endpoint is reachable and responds to authentication requests, indicating active session creation capability
  5. Audit recent session IDs for entropy weakness
    Generate a new API session and examine the session ID string format; if it appears as a 32-character hexadecimal MD5 hash with predictable patterns across multiple generations, it likely uses time-based construction
    Affected if Session IDs are 32-character hexadecimal strings exhibiting low entropy or correlating with generation timestamps

A user is affected if their Magento LTS version is below 20.18.0 AND the XML-RPC/SOAP API is enabled, allowing attackers to brute-force session IDs due to predictable time-based MD5 construction.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to Magento LTS 20.18.0 or later which implements CSPRNG for session ID generation. Consider invalidating all existing API sessions and implementing API rate-limiting as defense-in-depth.

Recommended fix High confidence

20.18.0

  1. 1. Verify current Magento LTS installation version by checking composer.json or the application's version endpoint
  2. 2. Back up the entire application database and filesystem before proceeding with any upgrade
  3. 3. Update composer dependencies to pull version 20.18.0 or later: `composer require magento/lts:^20.18.0 --no-update`
  4. 4. Run `composer update magento/lts` to install the fixed version
  5. 5. Clear all cached data and generated files: `rm -rf var/cache/* var/generation/* var/page_cache/*`
  6. 6. Run database schema upgrades if required: `php bin/magento setup:upgrade`
  7. 7. Re-compile the dependency injection configuration: `php bin/magento setup:di:compile`
  8. 8. Clear the production cache and verify the deployment: `php bin/magento cache:flush`
Caveat Review community release notes for any deprecated features or configuration changes between your current version and 20.18.0

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA3.0 h
21.0 hours of engineering $3,680
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-42155 in production — separate from our analysis above.

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What this is

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  • Version or environment caveats, and links to real fixes
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