{"id":"CVE-2026-107572","state":"PUBLISHED","title":"Inefficient Regular Expression Complexity in hMailServer","description":"Inefficient complexity in the Sieve filter evaluation of Progressive Robot hMailServer 6.2.24 through 6.3.5 allows an authenticated account holder to make the mail services unavailable with their own filter. A ':matches' pattern was matched by a backtracking descent whose time grew with the matched value's length raised to the number of wildcards, so a pattern such as '*a*a*a*b' over 800 characters took 44 seconds; and 'deleteheader' erased the fields it removed one at a time, so removing many fields of one name over a message's header cost O(N^2) (80,000 fields took 18.8 seconds). Sieve filters run on the small, shared delivery thread pool, so an account holder whose active script does this, fed a few messages they can send themselves, empties the pool and stops delivery for the whole server. The script is the account holder's own and cannot be set for another user.","publishedAt":"2026-10-08T11:46:41.080Z","updatedAt":"2026-10-08T17:35:21.719Z","severity":{"score":6.5,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","source":"GitLab"},"assigner":"GitLab","products":["Progressive Robot Ltd hMailServer"],"affected":[{"vendor":"Progressive Robot Ltd","product":"hMailServer","defaultStatus":"unaffected","versions":[{"version":"6.2.24","status":"affected","lessThan":"6.3.6","versionType":"semver"}],"repo":"https://gitlab.com/hmailserver/hmailserver"}],"references":["https://gitlab.com/hmailserver/hmailserver/-/work_items/75","https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6"],"weaknesses":["CWE-1333"],"ingestedAt":"2026-10-29T20:10:23.711Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/107xxx/CVE-2026-107572.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-107572","state":"PUBLISHED","datePublished":"2026-10-08T11:46:41.080Z","dateUpdated":"2026-10-08T17:35:21.719Z","assignerShortName":"GitLab","assignerOrgId":"ceab7361-8a18-47b1-92ba-4d7d25f6715a","dateReserved":"2026-10-08T10:51:25.637Z"},"containers":{"cna":{"title":"Inefficient Regular Expression Complexity in hMailServer","descriptions":[{"lang":"en","value":"Inefficient complexity in the Sieve filter evaluation of Progressive Robot hMailServer 6.2.24 through 6.3.5 allows an authenticated account holder to make the mail services unavailable with their own filter. A ':matches' pattern was matched by a backtracking descent whose time grew with the matched value's length raised to the number of wildcards, so a pattern such as '*a*a*a*b' over 800 characters took 44 seconds; and 'deleteheader' erased the fields it removed one at a time, so removing many fields of one name over a message's header cost O(N^2) (80,000 fields took 18.8 seconds). Sieve filters run on the small, shared delivery thread pool, so an account holder whose active script does this, fed a few messages they can send themselves, empties the pool and stops delivery for the whole server. The script is the account holder's own and cannot be set for another user."}],"affected":[{"vendor":"Progressive Robot Ltd","product":"hMailServer","defaultStatus":"unaffected","versions":[{"version":"6.2.24","status":"affected","lessThan":"6.3.6","versionType":"semver"}],"repo":"https://gitlab.com/hmailserver/hmailserver"}],"references":[{"url":"https://gitlab.com/hmailserver/hmailserver/-/work_items/75"},{"url":"https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6"}],"metrics":[{"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}],"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"HIGH","baseScore":6.5,"baseSeverity":"MEDIUM"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-1333","lang":"en","description":"CWE-1333: Inefficient Regular Expression Complexity","type":"CWE"}]}],"providerMetadata":{"shortName":"GitLab","orgId":"ceab7361-8a18-47b1-92ba-4d7d25f6715a","dateUpdated":"2026-10-08T11:46:41.080Z"},"solutions":[{"lang":"en","value":"Upgrade to hMailServer 6.3.6, which matches a ':matches' pattern by placing each piece once (time linear in the value times the pattern) and removes 'deleteheader' fields in one pass. Until then, review active Sieve scripts for ':matches' patterns with several wildcards and for 'deleteheader', and lower the maximum message size."}],"credits":[{"lang":"en","value":"Found in the hMailServer project's own security review (Progressive Robot Ltd)","type":"finder"}]},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-10-08T17:35:04.470485Z","id":"CVE-2026-107572","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-08T17:35:21.719Z"}}]}}}