---
id: CVE-2026-81638
title: >-
  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…
summary: >-
  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…
severity: low
cvss: 2.1
cvssVector: 'CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N'
cwe:
  - CWE-173
vendor: ash-project
product: ash_double_entry
affected:
  - ash_double_entry >= 0.1.0 < 1.0.19
  - >-
    ash-project/ash_double_entry >= 1e5f7ce8ff25f519c904731a29eb1258324e561a <
    d3e688d300a581ae214b3ca7d95ef4de63fbb050
published: '2026-09-07'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T15:18:49.077'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-81638'
references:
  - url: 'https://cna.erlef.org/cves/CVE-2026-81638.html'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ash-project/ash_double_entry/commit/d3e688d300a581ae214b3ca7d95ef4de63fbb050
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ash-project/ash_double_entry/security/advisories/GHSA-qxp2-vgp9-268q
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-81638'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-08T14:44:11.859893Z'
cvssSource: cna
epss: 0.00189
epssPercentile: 0.07568
ingestedAt: '2026-09-08T15:33:26.980Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.