---
title: "CVE-2026-42155: Magento LTS has Weak API Session ID — Predictable MD5 of Time-Derived Inputs"
url: https://erroneo.us/security/cve/CVE-2026-42155/
description: "CVE-2026-42155 (openmage/magento-lts (Composer (PHP))): Magento Long Term Support (LTS) is an unofficial, community-driven project provides an alternative…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-05-15
date_modified: 2026-05-15
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-42155"
kev: false
cvss: 9.3
epss: 0.00486
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-42155: Magento LTS has Weak API Session ID — Predictable MD5 of Time-Derived Inputs

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.5% , percentile 41: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 41% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes openmage/magento-lts (Composer (PHP)) <= 20.17.0, fixed in 20.18.0 . Check your lockfile, including transitive dependencies.

## What it is

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 Prior to 20.18.0, the XML-RPC / SOAP API session ID is generated using an outdated, time-based construction rather than a Cryptographically Secure Pseudo-Random Number Generator (CSPRNG).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.

## Affected packages

- Composer (PHP) `openmage/magento-lts` <= 20.17.0 → fixed: 20.18.0

## Affected products (CVE record)

- OpenMage magento-lts: < 20.18.0

## Severity

- GitHub_M CVSS 4.0: 9.3 `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`
- GitHub CVSS 4.0: 9.3 `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`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.49% probability of exploitation activity in the next 30 days; percentile 41.

## Sources

- [GitHub Advisory GHSA-2cwr-gcf9-pvxr](https://github.com/advisories/GHSA-2cwr-gcf9-pvxr)
- [CVE.org record CVE-2026-42155](https://www.cve.org/CVERecord?id=CVE-2026-42155)
- [NVD entry CVE-2026-42155](https://nvd.nist.gov/vuln/detail/CVE-2026-42155)
- [github.com](https://github.com/OpenMage/magento-lts/security/advisories/GHSA-2cwr-gcf9-pvxr)

---
Source page: https://erroneo.us/security/cve/CVE-2026-42155/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt