CVE-2026-27808 is a medium-severity server-side request forgery (SSRF) vulnerability in github.com/axllent/mailpit (go), affecting versions <= 1.29.1. It is fixed in 1.29.2.
Summary The Link Check API (/api/v1/message/{ID}/link-check) is vulnerable to Server-Side Request Forgery (SSRF). The server performs HTTP HEAD requests to every URL found in an email without validating target hosts or filtering private/internal IP addresses. The response returns status codes and status text per link, making this a non-blind SSRF. In the default configuration (no authentication on SMTP or API), this is fully exploitable remotely with zero user interaction. This is the same class of vulnerability that was fixed in the HTML Check API (CVE-2026-23845 / GHSA-6jxm-fv7w-rw5j) and the screenshot proxy (CVE-2026-21859 / GHSA-8v65-47jx-7mfr), but the Link Check code path was not included in either fix. Details The doHead() function in https://github.com/axllent/mailpit/blob/v1.29.0/internal/linkcheck/status.go#L59-L98 creates a plain http.Transport{} and http.Client with no DialContext hook or IP validation: The call chain is: GET /api/v1/message/{ID}/link-check hits LinkCheck() in https://github.com/axllent/mailpit/blob/v1.29.0/server/apiv1/other.go#L84 Which calls linkcheck.RunTests() in https://github.com/axllent/mailpit/blob/v1.29.0/internal/linkcheck/main.go#L16 Which extracts all URLs from the email's HTML (<a href>, <img src>, <link href>) and text body, then passes them to getHTTPStatuses() in https://github.com/axllent/mailpit/blob/v1.29.0/internal/linkcheck/status.go#L14 Which spawns goroutines calling doHead() for each URL with no filtering There is no check anywhere in this path to block requests to loopback (127.0.0.0/8), private (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), link-local (169.254.0.0/16), or IPv6 equivalents (::1, fc00::/7, fe80::/10). PoC Prerequisites: Mailpit running with default settings (no auth flags). A listener on 127.0.0.1:8081 simulating an internal service. Step 1, Start a listener to prove the SSRF: python3 -m http.server 8081 --bind 127.0.0.1 Step 2, Send a crafted email via SMTP: Step 3, Get the message ID: curl -s http://localhost:8025/api/v1/messages?limit=1 | jq -r '.messages[0].ID' Or use the shorthand ID latest. Step 4, Trigger the link check: curl -s http://localhost:8025/api/v1/message/latest/link-check | jq . Expected result: The Python HTTP server on port 8081 logs a HEAD /ssrf-proof request from Mailpit. The API response contains the status code and status text for each internal target: -- This behavior can be identified by creating a email txt file as Start a Python server on port 8408 execute the command mailpit sendmail < email.txt Observe a request to your python server and link status on the UI as OK The attacker now knows both internal services are reachable and gets their exact HTTP status codes, this allows internal port scanning Impact Who is impacted: Any Mailpit deployment where an attacker can both send email (SMTP) and access the API. This includes the default configuration, which binds both services to all interfaces with no authentication. What an attacker can do: Internal network scanning, Enumerate hosts and open ports on the internal network by reading status codes and error messages (connection refused vs. timeout vs. 200 OK). Cloud metadata access, Reach cloud provider metadata endpoints (169.254.169.254) and infer sensitive information from response codes. Service fingerprinting, Identify what services run on internal hosts from their HTTP status codes and response behavior. Bypass network segmentation, Use the Mailpit server's network position to reach hosts that are not directly accessible to the attacker. This is a non-blind SSRF: the attacker gets direct, structured feedback (status code + status text) for every URL, making exploitation straightforward without any timing or side-channel inference. Remediation Then standard Go library can be used to identify a local address being requested and deny it. And the safe dialer that uses it: Then the doHead() change, replace the bare transport with one that uses the safe dialer, and re-validate URLs on redirect hops: This fix should mitigate the reported SSRF.
Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.
CVE-2026-27808 has a CVSS score of 5.8 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment.
A fixed version is available (1.29.2). Upgrading removes the vulnerable code path.
go
github.com/axllent/mailpit (<= 1.29.1)github.com/axllent/mailpit → 1.29.2 (go)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Upgrade github.com/axllent/mailpit to 1.29.2 or later to resolve this vulnerability.
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CVE-2026-27808 is a medium-severity server-side request forgery (SSRF) vulnerability in github.com/axllent/mailpit (go), affecting versions <= 1.29.1. It is fixed in 1.29.2. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
CVE-2026-27808 has a CVSS score of 5.8 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
github.com/axllent/mailpit (go) versions <= 1.29.1 is affected.
Yes. CVE-2026-27808 is fixed in 1.29.2. Upgrade to this version or later.
Whether CVE-2026-27808 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
Upgrade github.com/axllent/mailpit to 1.29.2 or later.