CVE-2026-48991 XianYuLauncher: Legacy Microsoft account OAuth sign-in flow lacks PKCE and state validation
Attackers can intercept local OAuth flows to steal authentication tokens and take over user accounts due to missing PKCE and state validation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-48991?
CVE-2026-48991 is a medium-severity authentication bypass vulnerability in XianYuLauncher, published on 17 Jun 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-287
Which versions are affected by CVE-2026-48991?
How do I fix CVE-2026-48991?
No fix has been published for CVE-2026-48991 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-48991 being exploited?
There is no known exploitation of CVE-2026-48991 in the wild and no public exploit code.
Sources
Also known as GHSA-q6r9-qxmf-8hfx.