CVE-2021-36395Network attack vector

Service interruption via recursive repository URL parsing

Published Mar 6, 2023 · Updated Mar 7, 2025

Uncontrolled recursion in Moodle LMS 3.11, 3.10 through 3.10.4, and 3.9 through 3.9.7 allows remote attackers to interrupt service. The file repository URL parser recursively invokes cURL while resolving crafted repository URLs without sufficient recursion handling. No authentication or user interaction is required, and repeated recursive processing can exhaust server resources and make the site unavailable.

CVSS severity7.5
High
EPSS probability0.73%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uncontrolled recursion in Moodle LMS 3.11, 3.10 through 3.10.4, and 3.9 through 3.9.7 allows remote attackers to interrupt service. The file repository URL parser recursively invokes cURL while resolving crafted repository URLs without sufficient recursion handling. No authentication or user interaction is required, and repeated recursive processing can exhaust server resources and make the site unavailable.

The record

CVE
CVE-2021-36395
Published
Mar 6, 2023
Updated
Mar 7, 2025
Vendor
Moodle
Product
Moodle LMS
Classifications
CWE-674, CWE-400, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 6, 2023CVE publishedPublication date reported by the CVE source.
  2. Mar 7, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=3.11, 3.10 to 3.10.4, 3.9 to 3.9.7 and earlier unsupported versions

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Moodle · Moodle LMSversion=3.11, 3.10 to 3.10.4, 3.9 to 3.9.7 and earlier unsupported versions

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5CISA ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 11, 2026Sep 17, 2026
Latest reporting daySep 17, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-674Uncontrolled Recursion
CWE-400Uncontrolled Resource Consumption
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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