CVE-2026-82759: Reversible IP address pseudonymisation in AshAuthentication audit log hash mode

Severity: low (CVSS 1.8 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-17 · updated 2026-09-18
Weakness: CWE-760

Description

Use of a One-Way Hash with a Predictable Salt vulnerability in team-alembic AshAuthentication allows readers of the audit store to recover the client IP addresses that the audit log add-on's :hash privacy mode is meant to pseudonymise. AshAuthentication.AddOn.AuditLog.IpPrivacy.hash_ip/1 computes a single unkeyed :crypto.hash(:sha256, salt <> ip) and truncates the result to 16 hexadecimal characters. The salt is read from the :audit_log_ip_salt or :secret application config keys, and falls back to the constant "default-salt-change-in-production" published in the library source when neither is set, with nothing warning that the default is in use. The IPv4 space is only 2^32 values and SHA-256 is fast, so the whole hash table is precomputable and every stored value maps back to its source address. Truncating to 16 characters does not help, and even a configured salt leaves the hash cheap enough to enumerate once it leaks. This issue affects ash_authentication: from 4.12.0 before 4.15.0 and from 5.0.0-rc.0 before 5.0.0-rc.14.

Affected products

team-alembic ash_authentication: from 4.12.0 before 4.15.0; from 5.0.0-rc.0 before 5.0.0-rc.14 — fixed in 4.15.0, 5.0.0-rc.14

How to fix

Upgrade to a fixed version: team-alembic ash_authentication 4.15.0, 5.0.0-rc.14. Check the vendor advisory for mitigations.

References

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