{"id":"CVE-2026-21876","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-21876","generatedAt":"2026-10-31T07:04:11.823Z","title":"Only the last captured value is available to the chained rule, which means malicious charsets in earlier parts can be missed if a later part has a legitimate charset.","description":"The OWASP core rule set (CRS) is a set of generic attack detection rules for use with compatible web application firewalls. Prior to versions 4.22.0 and 3.3.8, the current rule 922110 has a bug when processing multipart requests with multiple parts. When the first rule in a chain iterates over a collection (like `MULTIPART_PART_HEADERS`), the capture variables (`TX:0`, `TX:1`) get overwritten with each iteration. Only the last captured value is available to the chained rule, which means malicious charsets in earlier parts can be missed if a later part has a legitimate charset. Versions 4.22.0 and 3.3.8 patch the issue.","published":"2026-01-08T14:15:57.000Z","lastModified":"2026-06-17T10:19:04.000Z","status":"Modified","sourceIdentifier":"security-advisories@github.com","cvss":{"version":"3.1","score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"},"cwe":["CWE-794"],"affected":["owasp/owasp modsecurity core rule set"],"epss":{"score":0.17745,"percentile":0.97158,"date":"2026-10-30","history":[]},"kev":{"listed":false},"exploits":{"count":1,"verified":false,"firstPublished":"2026-05-13","source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[{"edbId":52558,"kind":"exploit","title":"coreruleset 4.21.0 - Firewall Bypass","url":"https://www.exploit-db.com/exploits/52558","sourceUrl":"https://gitlab.com/exploit-database/exploitdb/-/blob/main/exploits/multiple/webapps/52558.py","file":"exploits/multiple/webapps/52558.py","published":"2026-05-13","added":"2026-05-13","updated":"2026-05-13","author":"anonimicerum","type":"webapps","platform":"multiple","port":null,"verified":false,"codes":["CVE-2026-21876"],"tags":null,"aliases":null,"applicationUrl":null,"screenshotUrl":null,"referenceUrl":null}]},"verdict":{"level":"urgent","text":"EPSS puts the probability of exploitation in the next 30 days at 17.7%, higher than 97% of all known CVEs. Patch or mitigate before the next change window."},"changes":[],"references":[{"url":"https://github.com/coreruleset/coreruleset/commit/80d80473abf71bd49bf6d3c1ab221e3c74e4eb83","tags":["Patch"],"source":"security-advisories@github.com"},{"url":"https://github.com/coreruleset/coreruleset/commit/9917985de09a6cf38b3261faf9105e909d67a7d6","tags":["Patch"],"source":"security-advisories@github.com"},{"url":"https://github.com/coreruleset/coreruleset/releases/tag/v3.3.8","tags":["Product","Release Notes"],"source":"security-advisories@github.com"},{"url":"https://github.com/coreruleset/coreruleset/releases/tag/v4.22.0","tags":["Product","Release Notes"],"source":"security-advisories@github.com"},{"url":"https://github.com/coreruleset/coreruleset/security/advisories/GHSA-36fv-25j3-r2c5","tags":["Exploit","Vendor Advisory"],"source":"security-advisories@github.com"},{"url":"https://github.com/daytriftnewgen/CVE-2026-21876","source":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-21876","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}