EUVD-2026-40428
GHSA-r799-c3x3-8633
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network-reachable proxy with low complexity, but requires an authenticated build-permission account (PR:L); high confidentiality/integrity impact via SSRF to admin endpoints, low availability, scope unchanged per advisory.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
Lifecycle Timeline
2DescriptionCVE.org
Capgo before 12.128.2 contains a path traversal vulnerability in the builder upload proxy that allows authenticated users with build permissions to bypass upload restrictions. Attackers can append traversal sequences to the upload path, which are normalized by the WHATWG URL parser, enabling access to internal administrative endpoints with the privileged BUILDER_API_KEY header and resulting in server-side privilege escalation.
AnalysisAI
Server-side privilege escalation in Capgo before 12.128.2 lets authenticated users holding build permissions abuse a path-traversal flaw in the builder upload proxy to reach internal administrative endpoints. By appending traversal sequences to the upload path - which the WHATWG URL parser normalizes - an attacker pivots requests carrying the privileged BUILDER_API_KEY header, turning limited build access into SSRF and elevated server-side privileges. Reported by VulnCheck with a CVSS 4.0 score of 8.7; no public exploit identified at time of analysis.
Technical ContextAI
Capgo is a live/over-the-air (OTA) update delivery service for Capacitor-based mobile apps; the affected component is its builder upload proxy, which forwards build artifacts to internal services. The root cause is CWE-22 (Improper Limitation of a Pathname to a Restricted Directory / path traversal): the proxy constructs an upstream URL from user-supplied path input, and the WHATWG URL parser collapses '../' traversal sequences, resolving the request to internal administrative endpoints rather than the intended upload target. Because these internal requests are issued with the trusted BUILDER_API_KEY header, the normalized path effectively grants the caller administrative authority - making this both a server-side request forgery (SSRF) and a privilege-escalation primitive. The single CPE provided, cpe:2.3:a:capgo:capgo, confirms the vendor/product but not granular version boundaries beyond the 'before 12.128.2' fix line.
RemediationAI
Vendor-released patch: 12.128.2 - upgrade Capgo to 12.128.2 or later, as referenced in GitHub Security Advisory GHSA-qprp-873h-mx6f (https://github.com/Cap-go/capgo/security/advisories/GHSA-qprp-873h-mx6f). If immediate upgrade is not possible, reduce exposure by restricting who holds build permissions (since exploitation requires an authenticated account with build rights) and by tightly scoping or rotating the BUILDER_API_KEY so the proxy cannot reach administrative endpoints with elevated trust; where feasible, place network controls between the upload proxy and internal admin services to block traversal-redirected requests. Note the trade-offs: revoking build permissions limits legitimate CI/build workflows, and network segmentation between the proxy and internal endpoints may break intended build-forwarding behavior, so validate against your deployment before enforcing. Consult the VulnCheck advisory (https://www.vulncheck.com/advisories/capgo-ssrf-and-privilege-escalation-via-path-traversal-in-builder-upload-proxy) for full technical detail.
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Same weakness CWE-22 – Path Traversal
View allSame technique Privilege Escalation
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External POC / Exploit Code
Leaving vuln.today