Live › vulnerability › CVE-2026-105963
Go to dashboardA failed type guard in plug_crypto makes the Erlang VM log a FunctionClauseError that carries the raw argument values, including the secret key base or the value an API key is compared against. An unauthenticated remote request can trigger it through Phoenix.Token.verify/4 or a missing header passed to secure_compare/2, and the secret then sits in application logs and error trackers.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-23 21:57 UTC. All times on this page are UTC.
Applications built on Phoenix or Plug that use Plug.Crypto token verification or secure_compare on request data, and that log errors with crash_reason metadata through Plug.Cowboy or Bandit. Exposure depends on logs being readable by someone who can reach them, since the request alone does not return the secret. Systems on plug_crypto 2.2.1 or plug 1.7.0 or later are not affected.
No product ranges from the sources yet.
mix.lock or with mix deps | grep plug_crypto; affected if below 2.2.1mix.lock; affected if from 1.6.3 up to but not including 1.7.02.2.1 or later1.7.0 or laterEach row is the first time that source carried this signal. The analyst’s rows are its own findings.
Externally-Generated Error Message Containing Sensitive Information vulnerability in plug_crypto in elixir-plug plug_crypto allows an unauthenticated remote attacker to expose the secret key base through application logs via a wrong-typed argument. Every public function in Plug.Crypto validates argument types in a function-head guard. A failed guard makes the Erlang VM raise FunctionClauseError with the actual argument values in the top stack frame, so the secret key base, a derived key, or the value an API key is compared against lands in that frame. The library's rescue blocks and Plug.Crypto.prune_args_from_stacktrace/1 only reach exceptions raised inside a function body, so they never see a guard failure. Plug.Cowboy and Bandit write the frame to the error log and attach it as crash_reason Logger metadata, which error trackers forward.
Two entry points take request data. Plug.Crypto.verify/4 exposes the secret key base when the token is neither a binary nor nil, which Phoenix.Token.verify/4 reaches because it forwards the token unguarded. Plug.Crypto.secure_compare/2 exposes the other operand when one side is not a binary, as happens when a missing request header yields nil. Reading the leaked value needs separate access to the logs or the error tracker, so the request alone does not disclose the secret to the attacker.
This issue affects plug: from 1.6.3 before 1.7.0; plug_crypto: from 1.0.0 before 2.2.1.
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