CVE-2026-82741 Ash.Type.Union with :map_with_tag does not force the tag on dump, enabling tag confusion

What is CVE-2026-82741?

CVE-2026-82741 is a low-severity vulnerability in ash-project ash, published on 1 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

Improper Validation of Specified Type of Input vulnerability in ash-project ash lets an attacker confuse the stored type tag of an Ash.Type.Union value that uses storage: :map_with_tag, bypassing that member's validation and any tag-based authorization.

For a union with storage: :map_with_tag, each member is identified in storage by a configured tag and tag_value. Ash.Type.Union.dump_to_native/2 (lib/ash/type/union.ex) did not force the configured tag when writing the value, so a tag carried in the submitted value was persisted verbatim. An attacker can therefore store a value whose data belongs to one member but whose tag names a different member. On read the value is re-selected by its tag and treated as the incompatible member (a type confusion), bypassing the real member's constraints and any logic or policy that branches on the union tag. The fix drops any incoming tag and forces the configured tag value on dump.

This issue affects ash: from 2.14.18 before 3.32.2.

Weakness: CWE-1287

Which versions are affected by CVE-2026-82741?

1 open source package ship an affected version, including ash.

How do I fix CVE-2026-82741?

Upgrade ash to 3.32.2 or later.

Is CVE-2026-82741 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-82741 exists.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as EEF-CVE-2026-82741, GHSA-2mmm-gc86-7jgg.