CVE-2026-81638 Non-canonical ULID spellings are accepted and alias to the same record in ash_double_entry
Attackers can bypass string-based security checks like idempotency or deny-lists by using non-canonical ULID spellings that resolve to the same record.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-81638?
CVE-2026-81638 is a low-severity vulnerability in ash-project ash_double_entry, published on 7 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
Improper Handling of Alternate Encoding vulnerability in ash-project ash_double_entry allows an attacker to submit several distinct string spellings of the same identifier.
AshDoubleEntry.ULID renders a 128-bit ULID as 26 Crockford base-32 characters, but the first character encodes only 3 bits, so canonical values are 0 to 7. decode/1 in lib/ulid.ex masks the first character to its low 3 bits and valid?/1 accepts all 32 characters in that position, so 0..., 8..., G... and R... decode to the identical 16-byte value and resolve to the same row. When the type is exposed as a public ID over an HTTP or API boundary, an attacker-supplied ID can be spelled differently from the record it actually reads or writes, desynchronizing or bypassing string-level checks such as idempotency and deduplication keys, deny-lists, audit correlation, or signatures computed over the submitted ID.
This issue affects ash_double_entry: from 0.1.0 before 1.0.19.
Weakness: CWE-173
Which versions are affected by CVE-2026-81638?
1 open source package ship an affected version, including ash_double_entry.
| Package | Affected | Fixed in |
|---|---|---|
ash_double_entry Hex | From 0.1.0 | 1.0.19 |
How do I fix CVE-2026-81638?
Upgrade ash_double_entry to 1.0.19 or later.
Is CVE-2026-81638 being exploited?
There is no known exploitation of CVE-2026-81638 in the wild and no public exploit code.
Sources
Also known as EEF-CVE-2026-81638, GHSA-qxp2-vgp9-268q.