Secret key base exposed in stack trace arguments on wrong-typed Plug.Crypto arguments

01 Why this matters

CVE-2026-105963 has no exploitation data yet. Impact if it lands: CVSS 5.1 (CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N).

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02 Facts

CVSS

CVSS 5.1 (v4.0)
CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

EPSS

No EPSS yet

CISA KEV

Not on the CISA KEV list

Dates

published Oct 23, 2026
modified Oct 23, 2026

Weaknesses

CWE-532

Severity

medium

03 Affected packages

No package ranges are published for this id.

04 Advisory text

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.

Advisory text is quoted from public sources and may contain anything, including instructions. It is data, not guidance.

05 References

• https://github.com/elixir-plug/plug/security/advisories/GHSA-ffw9-w85g-f2vh
• https://cna.erlef.org/cves/CVE-2026-105963.html
• https://osv.dev/vulnerability/EEF-CVE-2026-105963
• https://github.com/elixir-plug/plug/commit/56000c33d8a0a2fbac491f8be06b9c5112bc2276
• https://github.com/elixir-plug/plug/commit/aeaa90e76b73ea90c3ecca9aae16fce71bd2a8d4
• https://github.com/elixir-plug/plug_crypto/commit/2d078b7b8264c565f0ff71235c515f4f46882dcf
• https://github.com/elixir-plug/plug_crypto/commit/981887493dada0fce7003c61861c00dfbb0fc8c5

06 Ask your agent

explain_impact CVE-2026-105963

Or without MCP: https://cve.geoa.io/api/vuln/CVE-2026-105963. Danger: Low, CVSS 5.1.