CVE-2026-56329: Capgo - Cross-Tenant Preview Namespace Collision via Non-Bijective Underscore Decoding

Severity: medium (CVSS 6.4 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: 2026-07-10 · updated 2026-07-10
Weakness: CWE-436

Description

Capgo before 12.128.2 contains a cross-tenant preview namespace collision vulnerability caused by non-bijective decoding of double underscores to dots in preview hostname parsing. Attackers can register app IDs with underscores that collide with other tenants' dotted app IDs, causing preview misrouting and denial of preview access for victim applications.

Affected products

Capgo: before 12.128.2 — fixed in 12.128.2

How to fix

Upgrade to a fixed version: Capgo 12.128.2. Check the vendor advisory for mitigations.

References

https://github.com/Cap-go/capgo/security/advisories/GHSA-76qq-gg2p-pwwj
https://www.vulncheck.com/advisories/capgo-cross-tenant-preview-namespace-collision-via-non-bijective-underscore-decoding
https://github.com/Cap-go/capgo/security/advisories/GHSA-76qq-gg2p-pwwj

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