VulnerabilityPublished 7 Jan 2026

CVE-2026-21859: axllent mailpit · Server-Side Request Forgery (SSRF)

Affects axllent mailpitSource CVE Database V5

Not known to be exploited · public detection template (Nuclei) · CVSS 5.8 Medium : upgrade to 1.28.1 when convenient.

Data as of 26 Oct 2026, 11:42 UTC

CVSS 3.1 base score

5.8Medium

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

EPSS: 0.8% chance of exploitation in 30 days – higher than 56% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.28.1

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

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

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: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 7 Jan 2026
Detectable: evidence found.
nuclei template: Mailpit < 1.28.3 - Server-Side Request Forgery
Weaponised: 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 26 Oct 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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.

What to do

Upgrade mailpit and axllent/mailpit to 1.28.1.

Affected software

Product	Affected	Fixed in
axllentmailpit	Affected <1.28.1	Fixed in 1.28.1
GitHubaxllent/mailpit`pkg:github/axllent/mailpit`Other threats	Affected <1.28.1	Fixed in 1.28.1

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

AI-suggested

European organizations should immediately upgrade Mailpit to version 1.28.1 or later to apply the official fix that blocks internal IP addresses in the /proxy endpoint. Until the upgrade is possible, organizations should restrict access to the /proxy endpoint via network controls such as firewalls or API gateways, limiting it to trusted IP ranges or internal users only. Implement strict network segmentation to isolate development and testing tools like Mailpit from sensitive internal services. Monitor logs for unusual or unexpected requests to the /proxy endpoint that may indicate exploitation attempts. Additionally, conduct internal network scans to identify any exposed services that could be targeted via SSRF and apply appropriate access controls. Educate developers and DevOps teams about the risks of SSRF and secure coding practices for proxy or forwarding endpoints.

Description

Mailpit is an email testing tool and API for developers. Versions 1.28.0 and below have a Server-Side Request Forgery (SSRF) vulnerability in the /proxy endpoint, allowing attackers to make requests to internal network resources. The /proxy endpoint validates http:// and https:// schemes, but it does not block internal IP addresses, enabling attackers to access internal services and APIs. This vulnerability is limited to HTTP GET requests with minimal headers. The issue is fixed in version 1.28.1.

Impact

For European organizations, this SSRF vulnerability poses a moderate risk primarily related to unauthorized internal network reconnaissance and potential exposure of sensitive internal services. Attackers exploiting this flaw could access internal APIs, configuration endpoints, or management interfaces that are otherwise protected by network segmentation. This could lead to further lateral movement or information gathering for more advanced attacks. Organizations using Mailpit versions prior to 1.28.1 in development, testing, or staging environments connected to sensitive internal networks are particularly at risk. While the vulnerability does not directly compromise Mailpit’s integrity or availability, the indirect impact on internal network confidentiality could be significant, especially if critical infrastructure or sensitive data repositories are accessible internally. The risk is heightened in environments where Mailpit is exposed to untrusted networks or where network segmentation is weak.

CWE-918Server-Side Request Forgery (SSRF) (opens in a new tab)
Base weaknessCWE Top 25 (2025): #22OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.
OWASP Cheat Sheets
Server Side Request Forgery Prevention (opens in a new tab)
Unvalidated Redirects and Forwards (opens in a new tab)
Cross Site Scripting Prevention (opens in a new tab)
DOM based XSS Prevention (opens in a new tab)
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V12.6.1 (opens in a new tab)
V5.2.6 (opens in a new tab)
Attack patterns
Server Side Request Forgery (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 15 Jan 2026, 04:36 UTC

Public exploits and detectiona Nuclei detection template

WeaknessesCWE-918

Technical details

References

Community reviews

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