{"description":"Trending threats, MITRE ATT\u0026CK coverage, and detection metadata. Fed continuously.","feed_url":"https://feed.craftedsignal.io/products/coreruleset-4.21.0/feed.json","home_page_url":"https://feed.craftedsignal.io/","items":[{"_cs_actors":[],"_cs_cpes":[],"_cs_cves":[],"_cs_exploited":false,"_cs_has_poc":false,"_cs_poc_references":[],"_cs_products":["coreruleset (4.21.0)"],"_cs_severities":["high"],"_cs_tags":["firewall bypass","webapp"],"_cs_type":"advisory","_cs_vendors":[],"content_html":"\u003cp\u003eA public exploit (EDB-52558) has been published on Exploit-DB targeting a firewall bypass vulnerability in coreruleset version 4.21.0. The availability of this exploit code significantly elevates the risk to systems using this version of coreruleset, as it provides a readily available method for attackers to bypass security controls. This poses a threat to web applications protected by this ruleset, potentially leading to unauthorized access or data breaches. Defenders should prioritize reviewing configurations and applying necessary updates.\u003c/p\u003e\n\u003ch2 id=\"attack-chain\"\u003eAttack Chain\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003eAttacker identifies a web application protected by coreruleset 4.21.0.\u003c/li\u003e\n\u003cli\u003eAttacker crafts a malicious HTTP request designed to exploit the firewall bypass vulnerability.\u003c/li\u003e\n\u003cli\u003eThe crafted request is sent to the targeted web application.\u003c/li\u003e\n\u003cli\u003ecoreruleset 4.21.0 fails to properly sanitize or block the malicious request due to the bypass vulnerability.\u003c/li\u003e\n\u003cli\u003eThe malicious request is processed by the web application.\u003c/li\u003e\n\u003cli\u003eAttacker gains unauthorized access to sensitive data or functionality within the web application.\u003c/li\u003e\n\u003c/ol\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eSuccessful exploitation of this vulnerability allows attackers to bypass the intended security measures provided by coreruleset. This can lead to a range of impacts, including unauthorized access to sensitive data, modification of application functionality, or complete compromise of the protected web application. The public availability of an exploit increases the likelihood of widespread attacks targeting vulnerable systems.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003eUpgrade coreruleset to a patched version that addresses the firewall bypass vulnerability.\u003c/li\u003e\n\u003cli\u003eDeploy the Sigma rule \u003ccode\u003eDetect Coreruleset Firewall Bypass Attempt\u003c/code\u003e to your SIEM to identify potential exploitation attempts in web server logs.\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2026-05-13T13:03:46Z","date_published":"2026-05-13T13:03:46Z","id":"https://feed.craftedsignal.io/briefs/2026-05-coreruleset-firewall-bypass/","summary":"A firewall bypass vulnerability has been identified in coreruleset version 4.21.0, with a public exploit available on Exploit-DB, potentially increasing the risk of exploitation for unpatched systems.","title":"coreruleset 4.21.0 Firewall Bypass Vulnerability","url":"https://feed.craftedsignal.io/briefs/2026-05-coreruleset-firewall-bypass/"}],"language":"en","title":"CraftedSignal Threat Feed — Coreruleset (4.21.0)","version":"https://jsonfeed.org/version/1.1"}