CVE-2021-20185
Moodle Client side denial of service via personal message
It was found in Moodle before version 3.10.1, 3.9.4, 3.8.7 and 3.5.16 that messaging did not impose a character limit when sending messages, which could result in client-side (browser) denial of service for users receiving very large messages.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- None
- Availability
- Low
Exploit likelihood
What each source reports
NVD Score used
It was found in Moodle before version 3.10.1, 3.9.4, 3.8.7 and 3.5.16 that messaging did not impose a character limit when sending messages, which could result in client-side (browser) denial of service for users receiving very large messages.
- Record
CVE-2021-20185- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - CVSS 2.0
- 5.0 Medium
AV:N/AC:L/Au:N/C:N/I:N/A:P - Weakness
- CWE-400, CWE-770
- Updated
- 2026-11-02
CVE List No score
It was found in Moodle before version 3.10.1, 3.9.4, 3.8.7 and 3.5.16 that messaging did not impose a character limit when sending messages, which could result in client-side (browser) denial of service for users receiving very large messages.
- Record
CVE-2021-20185- Weakness
- CWE-400
- Updated
- 2026-11-02
EUVDEUVD-2022-3488 No score
It was found in Moodle before version 3.10.1, 3.9.4, 3.8.7 and 3.5.16 that messaging did not impose a character limit when sending messages, which could result in client-side (browser) denial of service for users receiving very large messages.
- Record
EUVD-2022-3488- Updated
- 2026-11-03
GitHub AdvisoriesGHSA-c3j6-33r4-89q3
Moodle Client side denial of service via personal message
It was found in Moodle before version 3.10.1, 3.9.4, 3.8.7 and 3.5.16 that messaging did not impose a character limit when sending messages, which could result in client-side (browser) denial of service for users receiving very large messages.
- Record
GHSA-c3j6-33r4-89q3- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - Weakness
- CWE-400, CWE-770
- Updated
- 2026-11-02
OSV
It was found in Moodle before version 3.10.1, 3.9.4, 3.8.7 and 3.5.16 that messaging did not impose a character limit when sending messages, which could result in client-side (browser) denial of service for users receiving very large messages.
- Record
CVE-2021-20185- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - Updated
- 2026-11-02
OSVGHSA-c3j6-33r4-89q3
Moodle Client side denial of service via personal message
It was found in Moodle before version 3.10.1, 3.9.4, 3.8.7 and 3.5.16 that messaging did not impose a character limit when sending messages, which could result in client-side (browser) denial of service for users receiving very large messages.
- Record
GHSA-c3j6-33r4-89q3- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - Weakness
- CWE-400, CWE-770
- Updated
- 2026-11-02
OSVUBUNTU-CVE-2021-20185
It was found in Moodle before version 3.10.1, 3.9.4, 3.8.7 and 3.5.16 that messaging did not impose a character limit when sending messages, which could result in client-side (browser) denial of service for users receiving very large messages.
- Record
UBUNTU-CVE-2021-20185- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - Updated
- 2026-11-02
OSVBIT-moodle-2021-20185 No score
It was found in Moodle before version 3.10.1, 3.9.4, 3.8.7 and 3.5.16 that messaging did not impose a character limit when sending messages, which could result in client-side (browser) denial of service for users receiving very large messages.
- Record
BIT-moodle-2021-20185- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
moodle/moodlePackagist |
3.5 up to 3.5.16 | 3.5.16 |
moodle/moodlePackagist |
3.8 up to 3.8.7 | 3.8.7 |
moodle/moodlePackagist |
3.9 up to 3.9.4 | 3.9.4 |
moodle/moodlePackagist |
3.10 up to 3.10.1 | 3.10.1 |
moodleBitnami |
3.5.0 up to 3.5.16, 3.8.0 up to 3.8.7, 3.9.0 up to 3.9.4, 3.10.0 up to 3.10.1 | 3.5.163.8.73.9.43.10.1 |
moodle/moodlePackagist |
3.5 up to 3.5.16, plus listed versions v3.5.0v3.5.0-betav3.5.0-rc1v3.5.1v3.5.10 Show 13 moreShow lessv3.5.11v3.5.12v3.5.13v3.5.14v3.5.15v3.5.2v3.5.3v3.5.4v3.5.5v3.5.6v3.5.7v3.5.8v3.5.9 |
3.5.16 |
moodle/moodlePackagist |
3.8 up to 3.8.7, plus listed versions v3.8.0v3.8.0-betav3.8.0-rc1v3.8.1v3.8.2 Show 4 moreShow lessv3.8.3v3.8.4v3.8.5v3.8.6 |
3.8.7 |
moodle/moodlePackagist |
3.9 up to 3.9.4, plus listed versions v3.9.0v3.9.0-betav3.9.0-rc1v3.9.0-rc2v3.9.0-rc3v3.9.1v3.9.2v3.9.3 |
3.9.4 |
moodle/moodlePackagist |
3.10 up to 3.10.1, plus listed versions v3.10.0v3.10.0-betav3.10.0-rc1v3.10.0-rc2 |
3.10.1 |
moodleUbuntu:Pro:16.04:LTS |
All versions, plus listed versions 2.7.9+dfsg-12.7.10+dfsg-12.7.11+dfsg-12.7.11+dfsg-22.7.12+dfsg-13.0.3+dfsg-0ubuntu13.0.3+dfsg-0ubuntu1+esm1 |
None known |
moodleUbuntu:Pro:18.04:LTS |
All versions, plus listed versions 3.0.3+dfsg-0ubuntu13.0.3+dfsg-0ubuntu1+esm1 |
None known |
History
| Recorded | Changed | Sources |
|---|---|---|
| facts | ||
| aliases | EUVD | |
| first indexed | CVE List, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2021-20185 is a medium vulnerability (CVSS 5.3) in Moodle, published January 28, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.39%, the 72nd percentile. Fixed in moodle/moodle 3.5.16.