CVE-2026-126623VulnerabilityPublished 11 Nov 2026

Inefficient Algorithmic Complexity

Source GCVE Database

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Authoritative record:CVE-2026-126623· High 7.5

Not known to be exploited · CVSS 7.5 High.

Data as of 11 Nov 2026, 10:04 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitLab)	CVSS 3.1	7.5

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 11 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 10 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-gxm7-28h3-vf9j

What to do

Affected software

Product	Affected	Fixed in
Progressive Robot LtdhMailServer	Affected >=6.3.6 <=6.3.7	Fixed in–
GitHubhmailserver/hmailserver`pkg:github/hmailserver/hmailserver`Other threats	Affected >=6.3.6 <=6.3.7	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Until a fix is available, administrators should consider disabling the REST API if not required, limit the acceptance of large TLS-RPT reports, and monitor for unusual mail delivery delays. Avoid enabling public base URLs for REST API links unless necessary.

Description

A vulnerability in Progressive Robot hMailServer versions 6.3.6 and 6.3.7 involves inefficient algorithmic complexity in the JSON reader. This flaw allows a remote unauthenticated attacker to cause denial of service by holding mail delivery threads or REST API worker threads, making mail delivery, REST API, and webmail unavailable. The issue arises from the JSON reader's handling of member names in a hash set that can be manipulated to degrade performance significantly. The attack surface includes TLS-RPT reports mailed to a hosted domain's report mailbox, REST API requests without authentication, webmail routes, and the send API. The vulnerability has a CVSS score of 7.5 (high severity).

Impact

The vulnerability allows remote unauthenticated attackers to cause denial of service by exhausting mail delivery threads and REST API worker threads. This results in unavailability of mail delivery, REST API, and webmail services. There is no impact on confidentiality or integrity reported. The CVSS score of 7.5 reflects a high severity denial of service impact with no privileges required and no user interaction.

Summary

The JSON reader in Progressive Robot hMailServer 6.3.6 and 6.3.7 suffers from inefficient algorithmic complexity due to the use of a standard library hash set for member names without a secret salt. An attacker can craft JSON objects with member names that collide in the same hash bucket, causing the reader's processing time to grow quadratically with the number of members. This leads to significant delays in reading large JSON objects (e.g., 16 MB objects taking several seconds), which can be exploited remotely without authentication. The attack vectors include sending large TLS-RPT reports to a report mailbox, REST API requests without authentication (if enabled), webmail routes, and API key usage. This results in denial of service by occupying mail delivery threads and REST API worker threads, disrupting mail delivery and service availability.

CWE-407Inefficient Algorithmic Complexity (opens in a new tab)
Class weaknessLikelihood of exploit: Low
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 11 Nov 2026, 10:04 UTC

WeaknessesCWE-407

Technical details

References

Community reviews

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