SB2020042821 - Multiple vulnerabilities in Zulip Server

Description

This security bulletin contains information about 3 secuirty vulnerabilities.

1) Cross-site scripting (CVE-ID: CVE-2020-9445)

The disclosed vulnerability allows a remote attacker to perform cross-site scripting (XSS) attacks.

The vulnerability exists due to insufficient sanitization of user-supplied data in the "modal_link" feature in the Markdown functionality. A remote attacker can trick the victim to follow a specially crafted link and execute arbitrary HTML and script code in user's browser in context of vulnerable website.

Successful exploitation of this vulnerability may allow a remote attacker to steal potentially sensitive information, change appearance of the web page, perform phishing and drive-by-download attacks.

2) Reverse Tabnabbing (CVE-ID: CVE-2020-9444)

The vulnerability allows a remote attacker to modify certain properties on the affected system. 

The vulnerability exist due to Reverse Tabnabbing in the Markdown functionality. A remote attacker can modify the location property to automatically redirect the user to a malicious site.

3) Stored cross-site scripting (CVE-ID: CVE-2020-10935)

The disclosed vulnerability allows a remote attacker to perform cross-site scripting (XSS) attacks.

The vulnerability exists due to insufficient sanitization of user-supplied data in a Markdown link. A remote attacker can inject and execute arbitrary HTML and script code in user's browser in context of vulnerable website.

Successful exploitation of this vulnerability may allow a remote attacker to steal potentially sensitive information, change appearance of the web page, perform phishing and drive-by-download attacks.

Remediation

Install update from vendor's website.

References

• https://blog.zulip.org/2020/04/01/zulip-server-2-1-3-security-release/
• https://www.coresecurity.com/advisories/zulip-account-takeover-stored-xss