Jenkins Assembla Plugin CVE-2026-57303

Exploitation requires that the attacker can control the HTTP/XML responses returned by the Assembla server that a Jenkins job is configured to communicate with - for example a compromised/malicious Assembla instance or a man-in-the-middle position on a non-validated or plaintext connection. The Assembla Plugin (≤1.4) must be installed and actively configured to contact an Assembla endpoint. Per the CVSS vector the attacker needs low privileges (PR:L), i.e. some authenticated/configuration foothold, and no user interaction is required. Limiting factors that reduce real-world risk: the dependence on controlling the server response (not a default, self-contained request), the need for the plugin to be installed and configured, and a confidentiality-focused impact with only low integrity and no availability effect; CISA SSVC rates exploitation as none and not automatable.

Signals are mixed and point to a real-but-conditional issue rather than a drop-everything emergency. The CVSS 3.1 vector (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N, 7.1 high) reflects network reach, low attacker privileges, high confidentiality impact and no availability impact. However, the description adds a hard precondition not fully captured by AC:L: the attacker must be able to control the responses of the configured Assembla server (e.g., a malicious/compromised Assembla endpoint or a man-in-the-middle position), which realistically raises attack complexity. CISA SSVC corroborates lower urgency: Exploitation 'none', Automatable 'no', Technical Impact 'partial'. KEV status is not listed (not actively exploited) and no POC is referenced. EPSS is not provided in the input, so widespread-exploitation probability cannot be quantified here. Net: a credible confidentiality/SSRF risk for environments using this plugin, but exploitation is gated on controlling the Assembla server response path, making it targeted rather than opportunistic.

An attacker who controls or impersonates the Assembla server configured in a Jenkins job (via a compromised endpoint or a man-in-the-middle on an unencrypted connection) returns a crafted XML payload containing a malicious external entity. When the Jenkins controller parses that response, the XXE entity reads a local secret file (e.g., credentials) or forces the controller to issue requests to internal systems (SSRF). No public exploit code is identified at time of analysis, and the attack hinges on influencing the Assembla response rather than a single unauthenticated request.