Mailpit - SSRF (CVE-2026-21859)

CVE-2026-21859 is a Server-Side Request Forgery (SSRF) vulnerability in Mailpit versions 1.28.0 and below, which allows remote attackers to exploit the /proxy endpoint to access internal network resources. By leveraging this flaw, attackers can send unauthorized HTTP GET requests to internal services and APIs, potentially exposing sensitive information or internal infrastructure details. The vulnerability is addressed in version 1.28.1.

CrowdSec has been tracking this vulnerability and its exploits since 11th of February 2026.

CrowdSec network data shows that most actors exploiting CVE-2026-21859 rely on broad, untargeted scans with minimal filtering. The activity is largely automated and opportunistic in nature. CrowdSec network telemetry also shows that exploitation of CVE-2026-21859 has significantly declined over the past week. Attack volumes are well below the long-term average, suggesting attackers are rapidly losing interest. The vulnerability appears to be falling out of active use across most threat landscapes.

Attackers exploit the /proxy endpoint by sending crafted requests with the url parameter targeting internal IP addresses, such as 127.0.0.1, to trigger server-side request forgery and access internal network resources.