Vulnerability-Lookup

GHSA-95HV-G278-W9P8

Vulnerability from github – Published: 2026-10-19 18:32 – Updated: 2026-10-19 18:32

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.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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{
  "affected": [],
  "aliases": [
    "CVE-2026-107569"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-606"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-19T16:17:01Z",
    "severity": "HIGH"
  },
  "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\u0027s 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.",
  "id": "GHSA-95hv-g278-w9p8",
  "modified": "2026-10-19T18:32:11Z",
  "published": "2026-10-19T18:32:11Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-107569"
    },
    {
      "type": "WEB",
      "url": "https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.7"
    },
    {
      "type": "WEB",
      "url": "https://gitlab.com/hmailserver/hmailserver/-/work_items/81"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-107569 (GCVE-0-2026-107569)

Vulnerability from cvelistv5 – Published: 2026-10-19 15:34 – Updated: 2026-10-20 19:27

Title

Unchecked Input for Loop Condition in hMailServer

Summary

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-10-20 19:27 UTC

CWE

CWE-606 - Unchecked Input for Loop Condition

Assigner

GitLab CNA under the mitre root

CNA scorecard C 74/100 over 327 records in the last 180 days details

References

2 references

URL	Tags
https://gitlab.com/hmailserver/hmailserver/-/work…
https://gitlab.com/hmailserver/hmailserver/-/rele…

Impacted products

1 product

Vendor	Product	Version
Progressive Robot Ltd	hMailServer	Affected: 6.0.0 , ≤ 6.3.6 (semver)

Credits

Found in the hMailServer project's own security review (Progressive Robot Ltd)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-107569",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-10-20T19:27:14.386515Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
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        "providerMetadata": {
          "dateUpdated": "2026-10-20T19:27:26.604Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "hMailServer",
          "repo": "https://gitlab.com/hmailserver/hmailserver",
          "vendor": "Progressive Robot Ltd",
          "versions": [
            {
              "lessThanOrEqual": "6.3.6",
              "status": "affected",
              "version": "6.0.0",
              "versionType": "semver"
            }
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        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Found in the hMailServer project\u0027s own security review (Progressive Robot Ltd)"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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\u0027s 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."
        }
      ],
      "metrics": [
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            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          },
          "format": "CVSS",
          "scenarios": [
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              "value": "GENERAL"
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              "cweId": "CWE-606",
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          "url": "https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.7"
        }
      ],
      "solutions": [
        {
          "lang": "en",
          "value": "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), holds a Sieve notify to the same limit, and refuses an account Sieve script or rule that edits the counter, and writes a line break in a header value as spaces unless it folds the line, so that no value a generated message is built from writes a field of its own. Until then there is no setting that stops the header being read or that turns Sieve off: reduce forwarding and auto-reply arrangements that can feed one another, keep the Sieve script surfaces closed to accounts (ManageSieveServerPort=0, the default, and the REST API off where it is not needed, RestApiPort=0, the default), review active Sieve scripts and account rules for a notify of the account\u0027s own address and for an edit of X-hMailServer-LoopCount, and watch the queue for a message generated far past the loop limit."
        }
      ],
      "title": "Unchecked Input for Loop Condition in hMailServer"
    }
  },
  "cveMetadata": {
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    "datePublished": "2026-10-19T15:34:37.492Z",
    "dateReserved": "2026-10-08T10:51:10.642Z",
    "dateUpdated": "2026-10-20T19:27:26.604Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
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}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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