SB2021112230 - Multiple vulnerabilities in Discourse

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Main Vulnerability Database SB2021112230

SB2021112230 - Multiple vulnerabilities in Discourse

Published: November 22, 2021 Updated: July 1, 2026

Security Bulletin ID SB2021112230
CSH Severity
Low
Patch available
YES
Number of vulnerabilities 3
Exploitation vector Remote access
Highest impact Data manipulation

Breakdown by Severity

Low 100%
  • Low
  • Medium
  • High
  • Critical

Description

This security bulletin contains information about 3 vulnerabilities.


1) Input validation error (CVE-ID: CVE-2021-42574)

CWE-ID: CWE-20 - Improper input validation

CVSSv4: CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/U:Clear


The vulnerability allows an attacker to bypass certain security checks.

The vulnerability exists in the Bidirectional Algorithm in the Unicode Specification. It permits the visual reordering of characters via control sequences, which can be used to craft source code that renders different logic than the logical ordering of tokens ingested by compilers and interpreters.

An attacker can leverage this behavior to encode source code for compilers accepting Unicode such that targeted vulnerabilities are introduced invisibly to human reviewers.


2) Improper access control (CVE-ID: CVE-2021-41263)

CWE-ID: CWE-284 - Improper Access Control

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:L/VA:L/SC:N/SI:N/SA:N/E:U/U:Clear


The vulnerability allows a remote user to disclose sensitive information and compromise the integrity of session handling.

The vulnerability exists due to improper access control in encrypted session cookies when re-using cookies between sites served by the same application instance. A remote user can re-use an encrypted session cookie from one site on another site served by the same application instance to disclose sensitive information and compromise the integrity of session handling.

Only multisite Discourse instances are vulnerable.


3) Use of Web Browser Cache Containing Sensitive Information (CVE-ID: CVE-2021-41271)

CWE-ID: CWE-525 - Use of Web Browser Cache Containing Sensitive Information

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U/U:Clear


The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to improper cache control in intermediate proxy caching behavior when handling a maliciously formed request. A remote attacker can send a specially crafted request to cause a denial of service.

The issue can cause an error response to be cached by intermediate proxies.


Remediation

Install update from vendor's website.

References