{"cve":"CVE-2021-41115","nvd":{"published":"2021-10-07T23:15:08.027","modified":"2026-06-17T04:07:54.053","status":"Modified","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).","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":6.5},"cwes":["CWE-1333","CWE-400"],"references":["https://github.com/zulip/zulip/commit/e2d303c1bb5f538d17dc3d9134bc8858bdece781","https://github.com/zulip/zulip/security/advisories/GHSA-4h36-mqfq-42jg","https://securitylab.github.com/advisories/GHSL-2021-118-zulip-zulip/","https://github.com/zulip/zulip/commit/e2d303c1bb5f538d17dc3d9134bc8858bdece781","https://github.com/zulip/zulip/security/advisories/GHSA-4h36-mqfq-42jg"],"products":["zulip:zulip"],"source":"nvd","synced_at":"2026-10-19T21:23:41.316049955+00:00"},"epss":{"cve":"CVE-2021-41115","score":0.01737,"percentile":0.77704,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}