Hysteria has an authenticated UDP ACL bypass that enables localhost and private-network UDP SSRF

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.4 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:L

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Summary Hysteria's UDP relay treats the destination address as packet-scoped, but ACL and outbound policy are applied only once when a new UDP session is created. After an authenticated client opens a UDP session using an allowed first destination, later packets in the same Session ID can be sent to different destinations without re-running ACL evaluation. This allows an authenticated user to bypass server-side UDP ACL rules and reach localhost or RFC1918/private-network UDP services from the server's network perspective, even when those destinations are explicitly rejected by ACL. Verified on current HEAD at commit 64c396385631579598cc29d5561bff98c439772f. Why this is a security issue This report is not based on the assumption that one UDP session must be bound to one destination. The protocol and official client both support per-packet destinations: - PROTOCOL.md:93-107 defines each UDPMessage as carrying its own Addr field. - core/client/udp.go:52-62 exposes Send(data, addr),…

Published by the source

26 Jun 2026, 19:48 UTC

Last modified by the source

26 Jun 2026, 19:48 UTC

Source last checked

26 Oct 2026, 15:24 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-vgrc-hq28-p3xp

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# Patch Next advisory brief: GHSA-vgrc-hq28-p3xp

Advisory: Hysteria has an authenticated UDP ACL bypass that enables localhost and private-network UDP SSRF
IDs: GHSA-vgrc-hq28-p3xp
Record: https://patchnext.com/advisories/ghsa-vgrc-hq28-p3xp (revision 1, source checked 26 Oct 2026, 15:24 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/apernet/hysteria/core/v2 2.9.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/apernet/hysteria/core/v2: affected >= 2.0.0, <= 2.9.1; fixed in 2.9.2

## Suggested inspection (read-only)
- Go github.com/apernet/hysteria/core/v2: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/apernet/hysteria/core/v2.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-vgrc-hq28-p3xp (GitHub-reviewed advisory GHSA-vgrc-hq28-p3xp lists affected ranges: Go github.com/apernet/hysteria/core/v2 >=2.0.0 <=2.9.1)

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