EEF-CVE-2026-82760 CVE-2026-82760 GHSA-q876-xr24-2mcx

Superlinear base62 decoding exhausts CPU and memory in AshAuthentication API key sign-in

Not rated yet Hex

Severity: 0.0 / 10; Unknown · CVSS 4.0
Exploit chance (EPSS): 0.74%; Chance of exploitation in the next 30 days. Higher than 54.50% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-407 Inefficient Algorithmic Complexity
Fix: 5.0.0-rc.14; Upgrade ash_authentication to this version or later

Description

Summary

Inefficient Algorithmic Complexity vulnerability in team-alembic AshAuthentication allows an unauthenticated attacker to exhaust CPU and memory via an oversized base62 segment in a submitted API key.

AshAuthentication.Base.decode62/1 in lib/ash_authentication/base.ex splits its argument into one binary per character and folds it with charval62/2, which recomputes Integer.pow(62, index) at every position instead of accumulating by Horner's method, so cost grows roughly cubically in the input length. bindecode62/1 in the same module is quadratic through Integer.undigits/2 and Integer.digits/2. Neither function caps byte_size/1, and AshAuthentication.Strategy.ApiKey.SignInPreparation passes the underscore-separated segments of the submitted key straight into both, before any key lookup and without prior authentication. The surrounding rescue clauses catch exceptions, not CPU or memory exhaustion.

This issue affects ash_authentication: from 4.8.0 before 4.15.0 and from 5.0.0-rc.0 before 5.0.0-rc.14.

Affected versions

Hex

Package	Vulnerable	Fixed in
ash_authentication	`>= 4.8.0, < 4.15.0` `>= 5.0.0-rc.0, < 5.0.0-rc.14`	`4.15.0` `5.0.0-rc.14`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

ash_authentication Hex → `5.0.0-rc.14`

mix

{:ash_authentication, "~> 5.0.0-rc.14"} # then: mix deps.update ash_authentication

Severity breakdown

CVSS 4.0 0.0

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Attack vector: Network
Attack complexity: Low
Attack requirements: Present
Privileges required: None
User interaction: None
Confidentiality (vulnerable system): None
Integrity (vulnerable system): None
Availability (vulnerable system): High
Confidentiality (subsequent systems): None
Integrity (subsequent systems): None
Availability (subsequent systems): None

Weakness

CWE-407: Inefficient Algorithmic Complexity

An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.

References

Advisories

github.com/team-alembic/ash_authentication/security/advisories/GHSA-q876-xr24-2mcx

Fixes and patches

Packages

hex.pm/packages/ash_authentication

Timeline

Sep 17, 2026 Published
Sep 18, 2026 Last updated by the source
Nov 1, 2026 Latest EPSS score

Advisory	Severity	Why it's related
EEF-CVE-2026-86688 Session id is not renewed on authentication in ash_authentication, allowing session fixation	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-76949 Remember-me sign-in guard reads a session key that is never written in ash_authentication, allowing session replacement	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-91039 dynamic_oidc identities are not namespaced by connection in ash_authentication, allowing cross-connection account takeover	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-88952 OAuth2 sign-in attached to an existing account without an email comparison in AshAuthentication	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-85500 `require_confirmed_with` is not enforced on the action and fails open on an unreadable attribute in AshAuthentication	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-86533 Revoked session accepted because the session jti is never checked in AshAuthentication and AshAuthentication Phoenix	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-81632 Single-use sign-in token placed in a redirect query string in AshAuthenticationPhoenix	Not rated yet	Also affects ash_authentication
EEF-CVE-2026-80218 Sign-in token minted for one resource accepted by another in AshAuthentication	Not rated yet	Also affects ash_authentication

Credits: James Harton, Jonatan Männchen / EEF, Peter Ullrich

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