CVE-2026-22689 is a medium-severity (CVSS 6.5) CWE-1385 vulnerability in github.com/axllent/mailpit. A fix is available for github.com/axllent/mailpit — see the affected versions and patch details below.
Mailpit is vulnerable to Cross-Site WebSocket Hijacking (CSWSH) allowing unauthenticated access to emails
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-22689.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-22689 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/axllent/mailpit🐹github.com/axllent/mailpitReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Summary The Mailpit WebSocket server is configured to accept connections from any origin. This lack of Origin header validation introduces a Cross-Site WebSocket Hijacking (CSWSH) vulnerability.
An attacker can host a malicious website that, when visited by a developer running Mailpit locally, establishes a WebSocket connection to the victim's Mailpit instance (default ws://localhost:8025). This allows the attacker to intercept sensitive data such as email contents, headers, and server statistics in real-time.
Vulnerable Code The vulnerability exists in server/websockets/client.go where the CheckOrigin function is explicitly set to return true for all requests, bypassing standard Same-Origin Policy (SOP) protections provided by the gorilla/websocket library.
Impact This vulnerability impacts the Confidentiality of the data stored in or processed by Mailpit. Although Mailpit is often used as a local development tool, this vulnerability allows remote exploitation via a web browser.
- Scenario: A developer has Mailpit running at localhost:8025.
- Trigger: The developer visits a malicious website (or a compromised legitimate site) in the same browser.
- Exploitation: The malicious site's JavaScript initiates a WebSocket connection to ws://localhost:8025/api/events. Since the origin check is disabled, the browser allows this cross-origin connection.
- Data Leak: The attacker receives all broadcasted events, including full email details (subjects, sender/receiver info) and server metrics.
Attack Impact
- Real-time notification of new emails
- Email metadata (sender, subject, recipients)
- Mailbox statistics
- All WebSocket broadcast data
Recommended Fix
The CheckOrigin function should be removed to allow gorilla/websocket to enforce its default safe behavior (checking that the Origin matches the Host). Alternatively, strict validation logic should be implemented.
Proposed Change (Remove unsafe check):
var upgrader = websocket.Upgrader{
ReadBufferSize: 1024,
WriteBufferSize: 1024,
// CheckOrigin: func(r *http.Request) bool { return true }, // REMOVED
EnableCompression: true,
}
Proof of Concept (PoC): To reproduce this vulnerability:
- Start Mailpit (default settings).
- Save the following HTML code as poc.html and serve it from a different origin (e.g., using python http.server on port 8000 or opening it directly as a file).
- Open the poc_websocket_hijack.html file in your browser.
- Send a test email to Mailpit or perform any action in the Mailpit UI.
- Observe that the "malicious" page successfully receives the event data.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/axllent/mailpit | ≥ 1.2.6&&< 1.28.2 | 1.28.2go get github.com/axllent/mailpit@v1.28.2 |
| 🐹Go | github.com/axllent/mailpit | all versions | 0.0.0-20260110031614go get github.com/axllent/mailpit@v0.0.0-20260110031614 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/axllent/mailpit, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/axllent/mailpit to 1.28.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-22689 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-22689 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-22689. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-22689 in your dependencies?
O3 Security finds CVE-2026-22689 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.