Hysteria vulnerable to server crash when max_datagram_frame_size very small

Exploitation

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

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Summary An authenticated client can crash the Hysteria server by advertising a very small QUIC maxdatagramframesize and then triggering a UDP response from the server. When the server tries to send the UDP response back via QUIC DATAGRAM, quic-go returns DatagramTooLargeError. The server then attempts to fragment the Hysteria UDP message, but the fragmentation code does not handle the case where the UDP message header itself is larger than the maximum datagram payload size. This results in a slice bounds panic and terminates the server process. Details The vulnerable path is the normal server-side UDP response path: In core/server/udp.go, receiveLoop packages a UDP response into a protocol.UDPMessage and calls sendMessageAutoFrag. If SendDatagram fails with quic.DatagramTooLargeError, sendMessageAutoFrag calls: However, FragUDPMessage in core/internal/frag/frag.go assumes that maxSize is greater than the UDP message header size: If an attacker-controlled client advertises a small…

Published by the source

26 Jun 2026, 19:58 UTC

Last modified by the source

26 Jun 2026, 19:58 UTC

Source last checked

26 Oct 2026, 15:24 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-qh5x-rfwf-rvfv

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# Patch Next advisory brief: GHSA-qh5x-rfwf-rvfv

Advisory: Hysteria vulnerable to server crash when max_datagram_frame_size very small
IDs: GHSA-qh5x-rfwf-rvfv
Record: https://patchnext.com/advisories/ghsa-qh5x-rfwf-rvfv (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 7.5)
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 2.9.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/apernet/hysteria: affected < 2.9.2; fixed in 2.9.2

## Suggested inspection (read-only)
- Go github.com/apernet/hysteria: 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.
- 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-qh5x-rfwf-rvfv (GitHub-reviewed advisory GHSA-qh5x-rfwf-rvfv lists affected ranges: Go github.com/apernet/hysteria >=0 <2.9.2)

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