MyBB up to 1.8.25 Message Parser cross site scripting

CVSS Meta Temp Score
CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.
Current Exploit Price (≈)
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CTI Interest Score
Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
4.6$0-$5k0.00

Summaryinfo

A vulnerability, which was classified as problematic, has been found in MyBB up to 1.8.25. This affects an unknown part of the component Message Parser. The manipulation leads to cross site scripting. This vulnerability is referenced as CVE-2021-27889. Remote exploitation of the attack is possible. Furthermore, an exploit is available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in MyBB up to 1.8.25 (Content Management System). It has been rated as problematic. This issue affects an unknown functionality of the component Message Parser. The manipulation with an unknown input leads to a cross site scripting vulnerability. Using CWE to declare the problem leads to CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Impacted is integrity.

The weakness was published 03/16/2021. The advisory is shared at github.com. The identification of this vulnerability is CVE-2021-27889. It demands that the victim is doing some kind of user interaction. Technical details are unknown but a public exploit is available. MITRE ATT&CK project uses the attack technique T1059.007 for this issue.

The exploit is available at packetstormsecurity.com. It is declared as proof-of-concept.

Upgrading to version 1.8.26 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Exploit-DB (49696). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

Name

Version

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔍
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 4.8
VulDB Meta Temp Score: 4.6

VulDB Base Score: 3.5
VulDB Temp Score: 3.2
VulDB Vector: 🔍
VulDB Reliability: 🔍

NVD Base Score: 6.1
NVD Vector: 🔍

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔍
VulDB Temp Score: 🔍
VulDB Reliability: 🔍

NVD Base Score: 🔍

Exploitinginfo

Class: Cross site scripting
CWE: CWE-79 / CWE-94 / CWE-74
CAPEC: 🔍
ATT&CK: 🔍

Physical: No
Local: No
Remote: Yes

Availability: 🔍
Access: Public
Status: Proof-of-Concept
Download: 🔍

EPSS Score: 🔍
EPSS Percentile: 🔍

Price Prediction: 🔍
Current Price Estimation: 🔍

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Exploit-DB: 🔍

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔍

Upgrade: MyBB 1.8.26

Timelineinfo

03/02/2021 🔍
03/16/2021 +14 days 🔍
03/16/2021 +0 days 🔍
05/04/2025 +1510 days 🔍

Sourcesinfo

Product: mybb.com

Advisory: github.com
Status: Confirmed

CVE: CVE-2021-27889 (🔍)
GCVE (CVE): GCVE-0-2021-27889
GCVE (VulDB): GCVE-100-171305
scip Labs: https://www.scip.ch/en/?labs.20161013

Entryinfo

Created: 03/16/2021 11:05
Updated: 05/04/2025 04:08
Changes: 03/16/2021 11:05 (38), 04/01/2021 19:52 (5), 04/01/2021 19:58 (18), 06/09/2024 00:27 (22), 12/21/2024 18:17 (1), 05/04/2025 04:08 (3)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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