# CVE-2026-82726: ash-project ash_phoenix regular expression tenant isolation bypass

Source: https://junglewise.ai/threats/cve-2026-82726-ash-project-ash-phoenix-regular-expression-tenant-isolation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-31. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-82726 · Severity: info · Published 2026-08-31

ash_phoenix is a web framework used to build multi-tenant applications that use subdomain-based tenant separation. A vulnerability in the subdomain extraction logic allows remote attackers to bypass tenant isolation and switch between tenants, or degrade application functionality, by sending a crafted Host header.

Technologies: [Ash-Project Ash Phoenix](https://junglewise.ai/threats/technologies/ash-phoenix). Vendors: [Ash-Project](https://junglewise.ai/threats/vendors/ash-project).

## Quick answers

**Is CVE-2026-82726 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-82726 being exploited in the wild.

**How severe is CVE-2026-82726?** Informational severity, published 31 August 2026.

**Which products and versions are affected?** Ash-Project Ash Phoenix 2.1.26 to before 2.3.25.

**Is there a fix for CVE-2026-82726?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-82726 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-82726?** Check whether you run Ash-Project Ash Phoenix at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability exists in the AshPhoenix.Helpers.get_subdomain/2 function, which uses String.replace with an unanchored, global regular expression to strip the root domain from the Host header. The root_host parameter is interpolated raw into the regex pattern without escaping, allowing metacharacters like . to be interpreted as wildcards. This permits attackers to craft malicious Host headers (e.g., "foo.exampleXcom.attacker.net" to extract "foo.attacker.net" instead of "foo") to select arbitrary tenants. Additionally, the comparison is case-sensitive, allowing bypass of tenant allowlists with uppercase variants. The attack requires only a network-accessible application and no authentication. The fix matches the root host case-insensitively and only as an exact trailing suffix.

## Affected products

- ash-project ash_phoenix 2.1.26 to before 2.3.25

## Timeline

- 2026-08-31: published

## References

- [https://repo.hex.pm/](https://repo.hex.pm/)
- [https://github.com/](https://github.com/)

## Related threats

- [ash-project ash_phoenix sensitive information in error messages](https://junglewise.ai/threats/cve-2026-82727-ash-project-ash-phoenix-sensitive-information-in-error-messages)
- [ash-project ash_phoenix authorization bypass through user-controlled key](https://junglewise.ai/threats/cve-2026-82725-ash-project-ash-phoenix-authorization-bypass-through-user)
- [ash-project ash_phoenix authorization bypass in SubdomainHook](https://junglewise.ai/threats/cve-2026-82724-ash-project-ash-phoenix-authorization-bypass-in-subdomainhook)