CVE-2021-41115: Regular expression denial-of-service in Zulip
First published: Thu Oct 07 2021(Updated: )
Zulip is an open source team chat server. In affected versions Zulip allows organization administrators on a server to configure "linkifiers" that automatically create links from messages that users send, detected via arbitrary regular expressions. Malicious organization administrators could subject the server to a denial-of-service via regular expression complexity attacks; most simply, by configuring a quadratic-time regular expression in a linkifier, and sending messages that exploited it. A regular expression attempted to parse the user-provided regexes to verify that they were safe from ReDoS -- this was both insufficient, as well as _itself_ subject to ReDoS if the organization administrator entered a sufficiently complex invalid regex. Affected users should [upgrade to the just-released Zulip 4.7](https://zulip.readthedocs.io/en/latest/production/upgrade-or-modify.html#upgrading-to-a-release), or [`main`](https://zulip.readthedocs.io/en/latest/production/upgrade-or-modify.html#upgrading-from-a-git-repository).
Credit: security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Zulip Desktop | <4.7 |
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Reference Links
Frequently Asked Questions
What is CVE-2021-41115?
CVE-2021-41115 is a vulnerability in Zulip, an open-source team chat server, that allows malicious organization administrators to create harmful links from users' messages.
How does CVE-2021-41115 impact Zulip?
CVE-2021-41115 allows organization administrators in Zulip to configure linkifiers that can create links from messages using regular expressions, which can be exploited by malicious administrators.
What is the severity rating of CVE-2021-41115?
CVE-2021-41115 has a severity rating of medium with a CVSS score of 6.5.
How can I fix CVE-2021-41115?
To fix CVE-2021-41115, it is recommended to update Zulip to a version that includes the fix provided by the Zulip team.
Are there any references for CVE-2021-41115?
Yes, you can find references for CVE-2021-41115 at the following links: [Reference 1](https://github.com/zulip/zulip/commit/e2d303c1bb5f538d17dc3d9134bc8858bdece781), [Reference 2](https://github.com/zulip/zulip/security/advisories/GHSA-4h36-mqfq-42jg), [Reference 3](https://securitylab.github.com/advisories/GHSL-2021-118-zulip-zulip/).
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