CVE-2026-81638
LowCVSS 2.1Exploitation Probability (EPSS)
Low risk3th percentile - higher than 3% of all known CVEs
Summary
A vulnerability in ash_double_entry of the ash-project allows an attacker to submit several distinct string spellings of the same ULID identifier. Due to improper masking of the first character, multiple strings decode to the same value, enabling desynchronization of string-level checks such as idempotency keys or deny-lists.
Risk Assessment
The risk includes bypassing security mechanisms based on string comparison, potentially leading to unauthorized access, data integrity issues, or business logic attacks.
Recommendation
It is recommended to upgrade ash_double_entry to version 1.0.19 or later, which includes the fix. Also consider server-side validation of identifiers to reject non-canonical representations.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS