CVE-2026-105963 Secret key base exposed in stack trace arguments on wrong-typed Plug.Crypto arguments
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-105963?
CVE-2026-105963 is a medium-severity vulnerability in elixir-plug plug, published on 23 Oct 2026.
Official description
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.
Weakness: CWE-532
Which versions are affected by CVE-2026-105963?
2 open source packages ship an affected version, including plug and plug_crypto.
| Package | Affected | Fixed in |
|---|---|---|
plug Hex | From 1.6.3 | 1.7.0 |
plug_crypto Hex | From 1.0.0 | 2.2.1 |
How do I fix CVE-2026-105963?
Upgrade plug to 1.7.0 or later.
Is CVE-2026-105963 being exploited?
There is no known exploitation of CVE-2026-105963 in the wild and no public exploit code.
Sources
Also known as EEF-CVE-2026-105963, GHSA-ffw9-w85g-f2vh.