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HTTP Response Splitting in Styx

Moderate severity GitHub Reviewed Published Feb 10, 2020 in ExpediaGroup/styx • Updated Jan 9, 2023

Package

maven com.hotels.styx:styx-api (Maven)

Affected versions

<= 1.0.0.beta8

Patched versions

1.0.0-rc1

Description

Vulnerability

Styx is vulnerable to CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting').

Vulnerable Component

The vulnerable component is the com.hotels.styx.api.HttpHeaders.Builder due to disabling the HTTP Header validation built into Netty in these locations:

https://github.com/HotelsDotCom/styx/blob/e1d578e9b9c38df9cd19c21dc2eb9b949d85b558/components/api/src/main/java/com/hotels/styx/api/HttpHeaders.java#L145

https://github.com/HotelsDotCom/styx/blob/e1d578e9b9c38df9cd19c21dc2eb9b949d85b558/components/api/src/main/java/com/hotels/styx/api/HttpHeaders.java#L145

new DefaultHttpHeaders(false) disables the built-in validation in Netty. Either use the default constructor or new DefaultHttpHeaders(true instead.

Additionally, another vulnerable component is the StyxToNettyResponseTranslator due to also disabling the HTTP Header validation built into netty in this location.

https://github.com/HotelsDotCom/styx/blob/8d60e5493e65d0d536afc0b350dcb02d24e0f7a7/components/server/src/main/java/com/hotels/styx/server/netty/connectors/StyxToNettyResponseTranslator.java#L30

DefaultHttpResponse nettyResponse = new DefaultHttpResponse(version, httpResponseStatus, false);
new DefaultHttpResponse(version, httpResponseStatus, false); disables the built-in validation in Netty. Please use the constructor new DefaultHttpResponse(version, httpResponseStatus, true);

Proof of Concept

The following test plugin proves that there is no header validation occurring.

    static class VulnerablePlugin implements Plugin {

        @Override
        public Eventual&lt;LiveHttpResponse&gt; intercept(LiveHttpRequest request, Chain chain) {
            String header = request.queryParam(&quot;header-value&quot;).get();
            LiveHttpRequest newRequest = request.newBuilder()
                .header(&quot;myRequestHeader&quot;, header)
                .build();
            return chain.proceed(newRequest).map(response -&gt;
                response.newBuilder().header(&quot;myResponseHeader&quot;, header).build()
            ) ;
        }

    }

    @Test
    public void simpleHeaderInjectionVulnerabilityPOC() {
        Plugin vulnerablePlugin = new VulnerablePlugin();
        // a simple way to mock the downstream system
        HttpInterceptor.Chain chain = request -&gt; {
            assertThat(request.header(&quot;myRequestHeader&quot;).orElse(null), is(&quot;test\r\nAnother: CRLF_Injection&quot;));
            return Eventual.of(response(OK).build());
        };

        // an example request you expect your plugin to receive
        String encodedGet = URLEncoder.encode(&quot;test\r\nAnother: CRLF_Injection&quot;);
        LiveHttpRequest request = get(&quot;/foo?header-value=&quot; + encodedGet)
            .build();

        // since this is a test, we want to wait for the response
        LiveHttpResponse response = Mono.from(vulnerablePlugin.intercept(request, chain)).block();

        assertThat(response.header(&quot;myResponseHeader&quot;).orElse(null), is(&quot;test\r\nAnother: CRLF_Injection&quot;));
    }

Additionally, if you run this LiveHttpResponse from this test through the StyxToNettyResponseTranslator::toNettyResponse, ideally, it would have caused an exception to be thrown. In its current state, it does not.

Similar Vulnerabilities

There have been reports of similar vulnerabilities in other popular libraries.

GHSA-35fr-h7jr-hh86 -> CVE-2019-16771
GHSA-mvqp-q37c-wf9j -> CVE-2019-17513

Finding

This vulnerability was found due to this query that Jonathan Leitschuh contributed to the Semmle QL project.
https://lgtm.com/rules/1510696449842/alerts/

References

@dvlato dvlato published to ExpediaGroup/styx Feb 10, 2020
Reviewed Mar 3, 2020
Published to the GitHub Advisory Database Mar 3, 2020
Last updated Jan 9, 2023

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

EPSS score

0.073%
(33rd percentile)

Weaknesses

CVE ID

CVE-2020-6858

GHSA ID

GHSA-6v7p-v754-j89v

Source code

No known source code

Credits

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