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No exploitation reportedAwaiting NVD analysis

CVE-2026-126613

Allocation of Resources Without Limits or Throttling in hMailServer

No exploitation reported by the sources we read.

  • Published2026-11-11
  • WeaknessCWE-770

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

Allocation of resources without limits in the JSON reader of Progressive Robot hMailServer 6.3.2 through 6.3.7 allows a remote attacker to exhaust the server's memory and hold its threads, making mail delivery, the REST API and the webmail unavailable. The reader built a tree of values far larger than the text it read, copying each value into every level above it, and set no bound on the number of values, so a single JSON document of many small values, within the 16 MB the server reads, raised the service's memory by about 2 GB and held one thread for seconds to minutes. From 6.3.4 a remote unauthenticated attacker reaches the reader by mailing such a document as a TLS-RPT report, up to 16 MB once decompressed, to a hosted domain's report mailbox, where an administrator has set one; it is read on a mail delivery thread (ten by default), and those threads deliver all mail, local and outbound. From 6.3.4 it is also reached without an account through the reply to a password-protected message, with the message's link alone, where the REST API is on (it is off by default) and a public base URL for such links is set; and by any account, from 6.3.2 through the webmail's send and draft routes and from 6.3.4 through its other routes granted 16 MB and the send API; the webmail's send, draft and settings routes parsed the body again for each member read. The REST API serves every request on four worker threads, in the process that also serves SMTP, IMAP and POP3, so a few such documents at once make it unavailable and can exhaust the machine's memory and end the whole service. This is a separate defect from CVE-2026-107574, the reader's handling of duplicate member names, fixed in 6.3.6.

Timeline

dates in UTC
  1. 2026-11-1108:31CVE publishedCNA

Versions per branch

Products declared by the CNA

As GitLab, the CNA that assigned this CVE, declared them in the CVE record; versions as written. NVD lists no product for this CVE yet: this is the only product data so far.

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2026-11-11

Neither OSV.dev nor the vendor advisories we read list affected versions for CVE-2026-126613 yet.

Full record on NVD

Fix

No fix published by the sources we read yet. NVD record

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Metasploit modules
none listed
Metasploit Framework

Sources

  • CNACVSS 3.17.52026-11-11
  • CNAweakness (CWE)CWE-7702026-11-11
  • NVDweakness (CWE)CWE-770read 2026-11-11

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published
2026-11-11
Last Modified
2026-11-11
NVD status
Received

Frequently asked questions

What is CVE-2026-126613?

Allocation of resources without limits in the JSON reader of Progressive Robot hMailServer 6.3.2 through 6.3.7 allows a remote attacker to exhaust the server's memory and hold its threads, making mail delivery, the REST API and the webmail unavailable. The reader built a tree of values far larger than the text it read, copying each value into every level above it, and set no bound on the number of values, so a single JSON document of many small values, within the 16 MB the server reads, raised the service's memory by about 2 GB and held one thread for seconds to minutes. From 6.3.4 a remote unauthenticated attacker reaches the reader by mailing such a document as a TLS-RPT report, up to 16 MB once decompressed, to a hosted domain's report mailbox, where an administrator has set one; it is read on a mail delivery thread (ten by default), and those threads deliver all mail, local and outbound. From 6.3.4 it is also reached without an account through the reply to a password-protected message, with the message's link alone, where the REST API is on (it is off by default) and a public base URL for such links is set; and by any account, from 6.3.2 through the webmail's send and draft routes and from 6.3.4 through its other routes granted 16 MB and the send API; the webmail's send, draft and settings routes parsed the body again for each member read. The REST API serves every request on four worker threads, in the process that also serves SMTP, IMAP and POP3, so a few such documents at once make it unavailable and can exhaust the machine's memory and end the whole service. This is a separate defect from CVE-2026-107574, the reader's handling of duplicate member names, fixed in 6.3.6.

Is CVE-2026-126613 actively exploited?

Active exploitation of CVE-2026-126613 has not been confirmed.

What is the CVSS score for CVE-2026-126613?

CVE-2026-126613 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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