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


- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 21 Oct 2026
- **Updated:** 21 Oct 2026
- **Also known as:** GHSA-26w4-8w32-4x3v

## What is CVE-2026-113799?

CVE-2026-113799 is a medium-severity vulnerability in abdolence slack-morphism-rust, published on 21 Oct 2026. 

### 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.

Weakness: CWE-532 (Insertion of Sensitive Information into Log File)

## Which versions are affected by CVE-2026-113799?

2 open source packages ship an affected version, including slack-morphism.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `slack-morphism` | crates.io | From 1.0.0 | 2.28.0 |
| `slack-morphism` | crates.io | From 1.0.0 | 2.28.0 |

## How do I fix CVE-2026-113799?

Upgrade slack-morphism to 2.28.0 or later.

## Is CVE-2026-113799 being exploited?

There is no known exploitation of CVE-2026-113799 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-113799 and fix it if it is affected.

What it is: CVE-2026-113799 is a medium-severity vulnerability in abdolence slack-morphism-rust, published on 21 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-113799 in the wild and no public exploit code.

Affected packages and fixed versions:
- slack-morphism (crates.io): affected from 1.0.0; fixed in 2.28.0
- slack-morphism (crates.io): affected from 1.0.0; fixed in 2.28.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-113799/ (Markdown: https://insights.sbomify.com/CVE-2026-113799/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-113799
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-113799
- OSV: https://osv.dev/vulnerability/CVE-2026-113799

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-113799/
Summaries are generated and may contain mistakes; the official description above is the record.