Portainer CE EUVD-2026-56003

Exploitation requires a valid Portainer CE user account at any privilege level - the vulnerability is not accessible to unauthenticated actors. The attacker must have HTTP access to the Portainer instance (AV:N per CVSS). No special non-default configuration is required; the flaw affects all standard Portainer CE deployments through 2.44.0 running the Docker proxy feature, which is a core default capability. The attack requires no user interaction (UI:N) and has low complexity (AC:L) once account access is obtained. Exploitation is limited by: (1) requirement for a valid (even low-privileged) Portainer account - organizations with strict user provisioning meaningfully reduce exposure; (2) network reachability of the Portainer management interface - instances restricted by VPN or IP allowlist limit the attacker population. No specific Docker host OS, container runtime version, or non-default Portainer setting is required to trigger the bypass.

CVSS 8.8 with AV:N/AC:L/PR:L/UI:N reflects a high-severity network-exploitable flaw requiring no interaction and low complexity - only a valid Portainer account is needed, which is a meaningful but modest barrier in environments with multiple users or shared access. The outcome (root-level Docker host access) is catastrophic, enabling full container control and host breakout. The provided vector marks S:U (no scope change), but granting root on the underlying Docker host arguably represents a cross-component impact exceeding Portainer's authorization boundary, suggesting S:C may be more precise. No EPSS score was provided, limiting probabilistic exploitation forecasting. No CISA KEV listing and no confirmed public POC reduce immediate urgency compared to a weaponized flaw, but the simplicity of path normalization bypass techniques means the attack is within reach of moderately skilled actors. The primary risk-limiting factor is PR:L: environments that enforce least-privilege Portainer access and restrict who holds user accounts materially reduce exposure. There are no conflicting signals, but absence of a formal vendor advisory is a gap - patch status cannot be confirmed.

An attacker holding a low-privileged Portainer account - obtained legitimately, via credential stuffing, or through phishing - sends a crafted HTTP request to the Portainer Docker proxy endpoint using a non-canonical URL path such as double-encoded slashes or percent-encoded separators. The authorization middleware evaluates the raw path, determines the request targets a non-privileged endpoint, and permits it; the Go HTTP proxy library canonicalizes the path before forwarding, and the Docker daemon receives and executes the intended privileged API call. The attacker thereby gains root-level control over the Docker host, enabling container escape, data exfiltration, or ransomware deployment on the underlying server. No public POC has been identified, but path normalization confusion is a well-understood technique and an exploit is within reach of any researcher familiar with HTTP proxy security.