Capgo EUVD-2026-40428

Exploitation requires an authenticated Capgo account that already holds build permissions (CVSS PR:L), and the target must be a Capgo instance before version 12.128.2 whose builder upload proxy uses the WHATWG URL parser to normalize the upload path and forwards requests with the BUILDER_API_KEY header. The attacker must be able to control the upload path value to inject '../' traversal sequences that resolve to internal administrative endpoints. Limiting factors: it is not exploitable by fully anonymous/unauthenticated users (a valid build-capable credential is needed) and is fixed in 12.128.2, but it requires no user interaction and only low attack complexity, so a single compromised or malicious build account suffices.

The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:L/UI:N) describes a network-reachable, low-complexity attack requiring low privileges and no user interaction, with high confidentiality and integrity impact (VC:H/VI:H) and low availability impact (VA:L); subsequent-system metrics are N, so the formal scoring treats impact as confined to the vulnerable system despite the privilege-escalation framing. The score of 8.7 (High) is credible for an authenticated attacker who already holds build permissions, which materially limits the attacker population versus a fully unauthenticated flaw. No EPSS score, KEV listing, or POC was provided in the input - so there is no evidence of active exploitation and no public exploit identified at time of analysis; the risk is driven by the severity and ease of the technique rather than by observed in-the-wild activity. Practically, prioritize this for any Capgo deployment where build accounts are issued to semi-trusted or numerous users, since the low privilege bar (PR:L) combined with full integrity/confidentiality impact makes it a strong escalation path for an insider or a compromised build account.

An attacker who already holds a Capgo account with build permissions crafts an upload request whose path contains '../' traversal sequences. The WHATWG URL parser normalizes the path so the proxy forwards the request - carrying the privileged BUILDER_API_KEY header - to an internal administrative endpoint, granting the attacker elevated server-side capabilities (SSRF). No public POC was provided, but the low attack complexity (AC:L) makes the technique straightforward to reproduce.