Denial of Service (DoS) Affecting github.com/rs/cors package, versions >=1.9.0 <1.11.0

Affected versions of this package are vulnerable to Denial of Service (DoS) through the processing of malicious preflight requests that include a Access-Control-Request-Headers header with excessive commas. An attacker can induce excessive memory consumption and potentially crash the server by sending specially crafted requests.

func BenchmarkPreflightAdversarialACRH(b *testing.B) {
    resps := makeFakeResponses(b.N)
    req, _ := http.NewRequest(http.MethodOptions, dummyEndpoint, nil)
    req.Header.Add(headerOrigin, dummyOrigin)
    req.Header.Add(headerACRM, http.MethodGet)
    req.Header[headerACRH] = adversarialACRH
    handler := Default().Handler(testHandler)

    b.ReportAllocs()
    b.ResetTimer()
    for i := 0; i < b.N; i++ {
        handler.ServeHTTP(resps[i], req)
    }
}

var adversarialACRH []string

func init() { // populates adversarialACRH
    n := int(math.Floor(math.Sqrt(http.DefaultMaxHeaderBytes)))
    commas := strings.Repeat(",", n)
    res := make([]string, n)
    for i := range res {
        res[i] = commas
    }
    adversarialACRH = res
}

Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.

Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.

One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.

When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.

Two common types of DoS vulnerabilities:

• High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.

• Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm ws package

• GitHub Commit
• GitHub Issue
• GitHub PR