# Note Mark: Username Enumeration via Login Endpoint Timing Side-Channel

Advisory record · `GHSA-w6m9-39cv-2fwp`

- **Identifiers:** `GHSA-w6m9-39cv-2fwp` · `CVE-2026-40263` · `GO-2026-5696`
- **State:** Confirmed
- **Severity:** CVSS 3.7 Low
- **Critical:** No
- **Weakness (CWE):** [CWE-208](https://cwe.mitre.org/data/definitions/208.html)
- **Tags:** [CWE-208](https://agentprime.io/advisories/tag/cwe-208.md)
- **Published:** 13 Apr 2026
- **Updated:** 25 Jun 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 13 Apr 2026, 19:31 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `github.com/enchant97/note-mark/backend` (Go): affected `<0.19.2-0.20260411145025-cf4c6f6acf70`; fixed in `0.19.2-0.20260411145025-cf4c6f6acf70`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Note Mark's Go backend (github.com/enchant97/note-mark/backend) is affected up to version 0.19.2-0.20260411145025-cf4c6f6acf70, and that same version is listed as the fix. The login endpoint responds more slowly for existing usernames because it runs a bcrypt password check, letting an unauthenticated network attacker tell whether a username exists. Upgrade to 0.19.2-0.20260411145025-cf4c6f6acf70 or later.

Written 6 Nov 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

- 3.7 Low, CVSS 3.1: `CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0026, the 17th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 15:06 UTC: First seen by agentprime
- 31 Oct 2026, 15:06 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-w6m9-39cv-2fwp)

## Sources

- [GitHub Advisory Database: GHSA-w6m9-39cv-2fwp](https://github.com/advisories/GHSA-w6m9-39cv-2fwp)
- [OSV: GHSA-w6m9-39cv-2fwp](https://osv.dev/vulnerability/GHSA-w6m9-39cv-2fwp)
- <https://github.com/enchant97/note-mark/security/advisories/GHSA-w6m9-39cv-2fwp>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-40263>
- <https://github.com/enchant97/note-mark/commit/cf4c6f6acf70b569d80396d323b067c00d45c034>
- <https://github.com/enchant97/note-mark>

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 (<https://api.agentprime.io/mcp>), 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: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-w6m9-39cv-2fwp>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-w6m9-39cv-2fwp/>. Everything for agents: <https://agentprime.io/llms.txt>.