Moodle Session Fixation allows unauthenticated users to hijack sessions via sesskey parameter

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.

Basic information

Type
reviewed
Severity
medium
Advisory on GitHub
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Repository advisory
Source code
Browse source ↗
Published (advisory)
2025-06-24 21:30:29 UTC
Updated
2025-06-26 14:12:36 UTC
GitHub reviewed
2025-06-26 14:12:34 UTC
NVD published
2025-06-24

EPSS Score

Score Percentile
0.29% 52.52%

CVSS Scores

Base score Version Severity Vector
4.2 3.1
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.

Identifiers

CWEs

CWE id Name
CWE-384 Session Fixation

Affected packages (1)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
composer moodle/moodle >= 3.0.0, <= 3.11.18 4.0.0

References

cvelogic Threat Intelligence