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.
CVE-2026-107569
“—” beside the score: it is equal to the CVSS score beside it.
Score 7.5 from GitHub Security Advisory (severity: HIGH) published 2026-10-19. A secondary CVSS source baseline 7.5; sources differ by 0.0.
Also known asEUVD-2026-104409 (ENISA EUVD) · GHSA-95hv-g278-w9p8 (GitHub Security Advisories)Source: ENISA EUVD
- High severity, but no confirmed exploitation yet
Upgrade to hMailServer 6.3.7, which reads X-hMailServer-LoopCount in one validated place (a count only when it is digits and never above the limit; anything else is read as the limit so no generated mail is made from it… (from the CVE record's solution, GitLab Inc.) — apply it.
- CVSS v3
- 7.5
- EG Score
- 7.5HIGHhigh confidence
- EG Risk
- 49EG Risk 49/100
EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.
How it’s computed (value × EchelonGraph’s weight)Severity75% × 45%Impact severity (EG Severity): CVSS 7.5 of 10. Never the KEV-floored or EPSS-lifted EG Score.Exploitation0.4% × 40%FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.Automatability100% × 15%CISA's SSVC Automatable value: yes (Vulnrichment).SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Attend at high (mission-essential systems).Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.Action: Upgrade to hMailServer 6.3.7, which reads X-hMailServer-LoopCount in one validated place (a count only when it is digits and never above the limit; anything else is read as the limit so no generated mail is made from it… (from the CVE record's solution, GitLab Inc.). Apply it within your standard update timelines at low or medium mission impact and sooner than that at high. - EPSS PROB
- 0.4%
- EPSS %ILE
- 31st
- KEV
- Not listed
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (7.5): severity, escalated by confirmed exploitation. This CVE's 7.5 is its impact severity (EG Severity), not escalated.
- EG Severity
- 7.5 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.4% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-27). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at low or medium mission impact; Attend at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; 60 days if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Attend at high (mission-essential systems).
Upgrade to hMailServer 6.3.7, which reads X-hMailServer-LoopCount in one validated place (a count only when it is digits and never above the limit; anything else is read as the limit so no generated mail is made from it… (from the CVE record's solution, GitLab Inc.). Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; 60 days if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it
Published
October 19, 2026
Last Modified
October 20, 2026
Advisory Details (2)
Auto-updated Oct 19, 2026Sieve and rule loop guard: an outside sender's X-hMailServer-LoopCount, read unbounded, and a Sieve notify that consulted no limit, let the generated-mail loop bound be escaped (6.0.0-6.3.6) (#81) · Issues · hmailserver / hMailServer · GitLab
https://gitlab.com/hmailserver/hmailserver/-/work_items/81hMailServer 6.3.7 · hmailserver / hMailServer · GitLab
https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.7Vendor Advisories for CVE-2026-107569(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 9× in last 7d / 25× in last 30d)
Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.
- 2026-11-01 16:33 UTCEPSS rescoreEPSS 0.4% · 31st percentile
- 2026-10-31 16:31 UTCEPSS rescoreEPSS 0.4% · 31st percentile
- 2026-10-30 16:33 UTCEPSS rescoreEPSS 0.4% · 31st percentile
- 2026-10-29 16:32 UTCEPSS rescoreEPSS 0.4% · 31st percentile
- 2026-10-28 16:31 UTCEPSS rescoreEPSS 0.4% · 31st percentile
- 2026-10-28 15:48 UTCEG score recompute
- 2026-10-28 15:48 UTCGHSA enrichmentGHSA-95hv-g278-w9p8 · GitHub severity HIGH · GitHub CVSS 7.5
- 2026-10-27 16:31 UTCEPSS rescoreEPSS 0.4% · 30th percentile
- 2026-10-26 16:30 UTCEPSS rescoreEPSS 0.4% · 30th percentile
- 2026-10-25 16:32 UTCEPSS rescoreEPSS 0.4% · 30th percentile
- 2026-10-25 14:54 UTCEG score recompute
- 2026-10-24 16:32 UTCEPSS rescoreEPSS 0.4% · 29th percentile
- 2026-10-23 16:31 UTCEPSS rescoreEPSS 0.4% · 29th percentile
- 2026-10-22 16:33 UTCEPSS rescoreEPSS 0.4% · 29th percentile
- 2026-10-21 16:32 UTCEPSS rescoreEPSS 0.4% · 29th percentile
- 2026-10-20 20:26 UTCEG score recompute
- 2026-10-20 20:26 UTCGHSA enrichmentGHSA-95hv-g278-w9p8 · GitHub severity HIGH · GitHub CVSS 7.5
- 2026-10-20 19:38 UTCEG score recompute
- 2026-10-20 19:38 UTCGHSA enrichmentGHSA-95hv-g278-w9p8 · GitHub severity HIGH · GitHub CVSS 7.5
- 2026-10-20 16:32 UTCEPSS rescoreEPSS 0.4% · 29th percentile
- 2026-10-19 21:36 UTCEG score recompute
- 2026-10-19 21:36 UTCGHSA enrichmentGHSA-95hv-g278-w9p8 · GitHub severity HIGH · GitHub CVSS 7.5
- 2026-10-19 16:31 UTCEG score recompute
- 2026-10-19 15:49 UTCEG score recomputeFirst assessed: 7.5 HIGH
- 2026-10-19 15:47 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Frequently asked(5)
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