CVE-2026-56296: Cap-go - App Existence Oracle via Unauthenticated transfer_app RPC

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-11 · updated 2026-10-25
Weakness: CWE-203

Description

Cap-go before 12.128.2 contains an information disclosure vulnerability in the public.transfer_app RPC function that returns distinct error messages for existing versus non-existing app IDs. Unauthenticated attackers can enumerate valid app IDs by observing error message differences when calling transfer_app with only the publishable API key.

Affected products

Cap-go capgo: before 12.128.2 — fixed in 12.128.2

How to fix

Upgrade to a fixed version: Cap-go capgo 12.128.2. Check the vendor advisory for mitigations.

References

https://github.com/Cap-go/capgo/security/advisories/GHSA-fmm3-3qcg-85j6
https://www.vulncheck.com/advisories/cap-go-app-existence-oracle-via-unauthenticated-transfer-app-rpc
https://github.com/Cap-go/capgo/security/advisories/GHSA-fmm3-3qcg-85j6

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