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Vulnerability · Published Oct 21, 2026 · Assigned by GitHub_M

CVE-2026-113799Slack Morphism verifier errors disclose valid HMACs in the logs

Medium 5.3

In plain English

A medium-severity sensitive data in logs in slack-morphism-rust from abdolence. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 38% of all known vulnerabilities).

Severity (CVSS 3.1)5.3Medium
Exploit odds (30 days)0.4%top 62.4% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

Official description

Slack Morphism is a client library for Slack Web/Events API/Socket Mode and Block Kit. Versions 1.0.0 through 2.27.0 expose the correct Slack request HMAC when signature verification fails. For an invalid request, `slack-morphism` computes the correct signature for the attacker-controlled timestamp and request body and stores it in `SlackEventWrongSignatureError.generated_hash`. The error's `Debug` and `Display` representations expose that value, and the default Axum listener error handler logs it at error level. An attacker who can both reach the application's Slack callback endpoint and read its application/service logs can therefore use the verifier as a chosen-message HMAC oracle. The attacker can send an arbitrary request with an invalid signature, recover the correct signature from the resulting log entry, and resend the same request within the five-minute freshness window. The second request passes Slack Morphism's signature verification and reaches the protected application callback without the attacker knowing the Slack signing secret. Version 2.28.0 patches the issue.

Affected products (as reported)

VendorProductVersions
abdolence slack-morphism-rust >= 1.0.0, < 2.28.0

Weakness: CWE-532 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N

References