CVE-2021-41115 Regular expression denial-of-service in Zulip
Malicious organization administrators can cause server denial-of-service by configuring complex regular expressions in linkifiers, requiring an upgrade to fix.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2021-41115?
CVE-2021-41115 is a medium-severity denial of service vulnerability in zulip, published on 7 Oct 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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).
Which versions are affected by CVE-2021-41115?
It affects 1 product.
Products include Zulip Zulip.
How do I fix CVE-2021-41115?
No fix has been published for CVE-2021-41115 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2021-41115 being exploited?
There is no known exploitation of CVE-2021-41115 in the wild and no public exploit code.
Other vulnerabilities in zulip
- CVE-2021-43799 RabbitMQ exposes ports with weak default secrets in Zulip Server
- CVE-2022-35962 Crafted link in Zulip message can cause disclosure of credentials
- CVE-2016-4427 Auth bypass in zulip
- CVE-2021-3866 Cross-site Scripting (XSS) - Stored in zulip/zulip
- CVE-2023-28623 Unauthorized user can register an account in specific configurations in Zulip
Sources
Also known as GHSA-4h36-mqfq-42jg.