{"id":"CVE-2026-107569","summary":"Unchecked Input for Loop Condition in hMailServer","details":"Unchecked input for a loop condition in Progressive Robot hMailServer 6.0.0 through 6.3.6 allows a remote unauthenticated attacker to stop the server carrying mail. The server bounds the mail it generates in response to a message - a rule forward, reply or copy, an account forward, a Sieve redirect, vacation or notify, a bounce, an out-of-office reply - by a counter it carries in the message's X-hMailServer-LoopCount header, and makes no more once the counter reaches the configured rule loop limit (5 by default); that is what ends a forwarding or auto-reply cycle in a bounded number of hops. X-hMailServer-LoopCount is an ordinary header that is not stripped from mail arriving from outside, and the server read it with a signed conversion and no validation, so a count below zero passed every test against the limit: a sender who sets X-hMailServer-LoopCount to a negative value, or on the Linux builds to a value above the 32-bit signed range that the conversion wraps to a negative one, lifts the bound, and a message that enters a generated-mail cycle then loops up to about two thousand million times, each hop a queued message and a delivery, filling the queue and disk and stopping mail service. The Sieve notify action (from 6.2.22) consulted no limit at all, and its increment of the count could overflow a signed integer; and an account could reset the counter on its own mail through a Sieve editheader of the header (from 6.2.22) or a rule Set header value action (all versions) ahead of a forward or redirect.","modified":"2026-10-20T02:46:34.007877030Z","published":"2026-10-19T15:34:37.492Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/107xxx/CVE-2026-107569.json","cna_assigner":"GitLab","cwe_ids":["CWE-606"]},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/107xxx/CVE-2026-107569.json"},{"type":"PACKAGE","url":"https://gitlab.com/hmailserver/hmailserver"},{"type":"WEB","url":"https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.7"},{"type":"WEB","url":"https://gitlab.com/hmailserver/hmailserver/-/work_items/81"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-107569"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://gitlab.com/hmailserver/hmailserver","events":[{"introduced":"e4b7163189ac6ce365bb954cf3e264e2e3105a18"},{"last_affected":"e3c448aa66fc310b74d076884d54fae951296915"}],"database_specific":{"extracted_events":[{"introduced":"6.0.0"},{"last_affected":"6.3.6"}],"source":"AFFECTED_FIELD"}}],"versions":["v6.3.6","v6.3.5","v6.3.4","v6.3.3","v6.3.2","build-inputs-1","v6.3.1","v6.3.0","v6.2.28","v6.2.27","v6.2.26","v6.2.25","v6.2.24","v6.2.23-alpha2","v6.2.23-alpha1","v6.2.22-pre6","v6.2.22-pre5","v6.2.22-pre4","v6.2.22-pre3","v6.2.22-pre2","v6.2.22-pre1","v6.2.21","v6.2.20","v6.2.19","v6.2.18","v6.2.17","v6.2.16","v6.2.15","v6.2.14","v6.2.13","v6.2.12","v6.2.11","v6.2.10","v6.2.9","v6.2.8","v6.2.7","v6.2.6","v6.2.5","v6.2.4","v6.2.3","v6.2.2","v6.2.1","v6.2.0","v6.1.0","v6.0.0-B4","v6.0.0-B3","v6.0.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-107569.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"}]}