CVE-2026-54617: LaunchServer FileServerHandler has an unauthenticated path traversal issue

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 2.9%, percentile 87: FIRST’s model estimates a 2.9% chance of exploitation activity in the next 30 days, higher than 87% of all scored CVEs (elevated). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes pro.gravit.launcher:launchserver-api (Maven) <= 5.7.11, no fixed version listed. Check your lockfile, including transitive dependencies.

What it is

GravitLauncher is an open-source Minecraft launcher based on sashok724's v3. Prior to 5.7.12, an unauthenticated remote actor can send a raw HTTP request target without a leading slash to the default LaunchServer file server on port 9274. FileServerHandler.channelRead0 in components/launchserver/src/main/java/pro/gravit/launchserver/socket/handlers/fileserver/FileServerHandler.java strips the first request-target character and resolves the remaining path against updatesDir without re-normalizing and verifying containment. This leaves parent-directory components in a no-leading-slash request and allows reading any file accessible to the LaunchServer process, including .keys/ecdsaid, .keys/legacySalt, and LaunchServer.json. Disclosure of those files can expose signing keys, refresh-token material, and database credentials, enabling forged administrative access tokens and full authentication bypass. A normalizing L7 proxy may block the primary request form, but direct exposure and L4/TCP proxies remain affected, and netty.fileServerEnabled is enabled by default. This issue is fixed in 5.7.12.

From the GitHub advisory

Summary An unauthenticated path traversal in the LaunchServer HTTP file server (FileServerHandler) lets any remote actor read any file readable by the LaunchServer process (e.g. ../../../../etc/passwd). This is a generic arbitrary-file-read primitive, so the fix must address the traversal itself, not any specific file.

The readable files include the server's own secrets, which turns this from information disclosure into full compromise: the ECDSA private key that signs access JWTs (.keys/ecdsaid), the refresh-token salt (.keys/legacySalt), and LaunchServer.json (database credentials). With the signing key an attacker mints a valid access token for any account, including admins. That is a full authentication bypass. Pre-auth, default config, port 9274.

Affected: GravitLauncher LaunchServer ≤ 5.7.11 (the LaunchServer application; the published pro.gravit.launcher:-api Maven artifacts do not contain the vulnerable code).

Details In FileServerHandler.channelRead0:

substring(1) blindly strips a leading slash, assuming the request-target always starts with /. Netty's HttpServerCodec accepts a request-target without a leading slash verbatim (decoderResult().isSuccess() == true). For such a target, normalize() cannot collapse the leading .., substring(1) turns ../ into ./ (leaving the remaining ..), and base.resolve(path), which is not re-normalized, resolves outside updatesDir.

Weakness type: CWE-22, CWE-200, CWE-522.

Product: pro.gravit.launcher:launchserver-api (Maven) · Assigned by: GitHub_M · Published: 2026-09-17

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 2.88% probability of exploitation activity in the next 30 days; percentile 87.

Timeline

• 2026-07-02 — GitHub-reviewed advisory GHSA-5g75-477j-2c2f published (critical)
• 2026-09-17 — CVE record published by GitHub_M
• 2026-09-18 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-5g75-477j-2c2f github.com
2. CVE.org record CVE-2026-54617 cve.org
3. NVD entry CVE-2026-54617 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

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