{"id":"EEF-CVE-2026-81638","summary":"Non-canonical ULID spellings are accepted and alias to the same record in ash_double_entry","details":"## Summary\n\nImproper Handling of Alternate Encoding vulnerability in ash-project ash_double_entry allows an attacker to submit several distinct string spellings of the same identifier.\n\n`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.\n\nThis issue affects ash_double_entry: from 0.1.0 before 1.0.19.\n\n## Configurations\n\nReachable only when an application exposes `AshDoubleEntry.ULID` as a public identifier over an HTTP or API boundary and performs string-level checks on the submitted ID (idempotency or deduplication keys, deny-lists, audit correlation, or signatures) rather than treating the value as opaque.","aliases":["CVE-2026-81638","GHSA-qxp2-vgp9-268q"],"modified":"2026-09-08T22:45:03.325254394Z","published":"2026-09-07T22:33:29.297Z","database_specific":{"capec_ids":["CAPEC-267"],"cpe_ids":["cpe:2.3:a:ash-project:ash_double_entry:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-173"]},"references":[{"type":"ADVISORY","url":"https://github.com/ash-project/ash_double_entry/security/advisories/GHSA-qxp2-vgp9-268q"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-81638.html"},{"type":"FIX","url":"https://github.com/ash-project/ash_double_entry/commit/d3e688d300a581ae214b3ca7d95ef4de63fbb050"},{"type":"PACKAGE","url":"https://hex.pm/packages/ash_double_entry"}],"affected":[{"package":{"name":"ash_double_entry","ecosystem":"Hex","purl":"pkg:hex/ash_double_entry"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.1.0"},{"fixed":"1.0.19"}]}],"versions":["0.1.0","0.1.1","0.1.2","0.2.0","0.2.1","0.2.2","0.2.3","0.2.4","1.0.0","1.0.0-rc.0","1.0.1","1.0.10","1.0.11","1.0.12","1.0.13","1.0.14","1.0.15","1.0.16","1.0.17","1.0.18","1.0.2","1.0.3","1.0.4","1.0.5","1.0.6","1.0.7","1.0.8","1.0.9"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-81638.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/ash-project/ash_double_entry","events":[{"introduced":"1e5f7ce8ff25f519c904731a29eb1258324e561a"},{"fixed":"d3e688d300a581ae214b3ca7d95ef4de63fbb050"}]}],"versions":["v1.0.18","v1.0.17","v1.0.16","v1.0.15","v1.0.14","v1.0.13","v1.0.12","v1.0.11","v1.0.10","v1.0.9","v1.0.8","v1.0.7","v1.0.6","v1.0.5","v1.0.4","v1.0.3","v1.0.2","v1.0.1","v1.0.0","v1.0.0-rc.1","v1.0.0-rc.0","v0.2.4","v0.2.3","v0.2.2","v0.2.1","v0.2.0","v0.1.2","v0.1.1","v0.1.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-81638.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"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"}],"credits":[{"name":"Peter Ullrich","type":"FINDER"},{"name":"Peter Ullrich","type":"REPORTER"},{"name":"Zach Daniel / Ash Project","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"COORDINATOR"}]}