EUVD-2026-107388Published

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 …

Exact source revision recorded 5 Nov 2026 04:02:50 UTC. It does not establish the source's current position. Latest evidence.

Recorded JSON

euvd · EUVD-2026-107388

Published

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.

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datePublished: Oct 21, 2026, 4:15:10 PM

dateUpdated: Oct 30, 2026, 3:14:24 PM

Source published: Oct 21, 2026, 4:15:10 PM (timezone not stated)
Source modified: Oct 30, 2026, 3:14:24 PM (timezone not stated)
Observed here: 5 Nov 2026 04:02:50 UTC
Source terms: ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N