# Authlib accepts an empty HMAC key, allowing JWS/JWT signature forgery (HS256/HS384/HS512) Advisory record · `GHSA-8m4g-j4wp-wgcg` - **Identifiers:** `GHSA-8m4g-j4wp-wgcg` · `CVE-2026-114616` · `PYSEC-2026-4356` - **State:** Confirmed - **Severity:** CVSS 7.4 High - **Critical:** No - **Weakness (CWE):** [CWE-287](https://cwe.mitre.org/data/definitions/287.html) · [CWE-326](https://cwe.mitre.org/data/definitions/326.html) · [CWE-1391](https://cwe.mitre.org/data/definitions/1391.html) - **Tags:** [Authentication bypass](https://agentprime.io/advisories/tag/auth-bypass.md) · [Weak cryptography or TLS](https://agentprime.io/advisories/tag/weak-crypto.md) · [Hard-coded credentials](https://agentprime.io/advisories/tag/hard-coded-credentials.md) - **Published:** 27 Oct 2026 - **Updated:** 30 Oct 2026 - **Reviewed by a person:** No Published by the GitHub Advisory Database at 27 Oct 2026, 16:09 UTC. agentprime has not analysed this yet, so whether it affects any app is not known. ## Affected packages - `authlib` (PyPI): affected `<1.9.1`; fixed in `1.9.1` ## Machine-written summary Summary written by Claude Haiku from the source advisory. Not reviewed by a person. > Authlib versions before 1.9.1 accept an empty symmetric (oct) key for HMAC signing and verification with HS256, HS384 and HS512, so a token signed with that empty key is accepted as valid. An attacker who can get an application to verify tokens with an empty key, for example when a secret is read from an unset environment variable defaulting to an empty string, can forge tokens with arbitrary claims. The advisory states the issue was fixed in 1.9.1, so upgrade authlib to version 1.9.1 or later. Written 31 Oct 2026. ## Not analysed yet We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check. ## Severity and exploitation - 7.4 High, CVSS 3.1: `CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N`, from CNA (GitHub_M) - **CISA KEV:** Not listed. - **EPSS:** 0.0030, the 22nd percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days. ## Timeline - 31 Oct 2026, 14:07 UTC: First seen by agentprime - 31 Oct 2026, 14:07 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-8m4g-j4wp-wgcg) ## Sources - [GitHub Advisory Database: GHSA-8m4g-j4wp-wgcg](https://github.com/advisories/GHSA-8m4g-j4wp-wgcg) - [OSV: GHSA-8m4g-j4wp-wgcg](https://osv.dev/vulnerability/GHSA-8m4g-j4wp-wgcg) - - - - - Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code. ## Check whether this affects you A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet. - With the agentprime MCP server (), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: - In a browser: reads your lockfile in the browser, never uploading it. - Whether it touches your code, with file and line: the Claude Code plugin, - As JSON: , or `POST https://api.agentprime.io/v1/match` with your packages () --- The web page: . Everything for agents: .