SynopsisApache 2.4.x < 2.4.25 Multiple Vulnerabilities (httpoxy)
DescriptionAccording to its banner, the version of Apache running on the remote host is 2.4.x prior to 2.4.25. It is, therefore, affected by the following vulnerabilities :
- A flaw exists in the mod_session_crypto module due to encryption for data and cookies using the configured ciphers with possibly either CBC or ECB modes of operation (AES256-CBC by default). An unauthenticated, remote attacker can exploit this, via a padding oracle attack, to decrypt information without knowledge of the encryption key, resulting in the disclosure of potentially sensitive information. (CVE-2016-0736)
- A denial of service vulnerability exists in the mod_auth_digest module during client entry allocation. An unauthenticated, remote attacker can exploit this, via specially crafted input, to exhaust shared memory resources, resulting in a server crash. (CVE-2016-2161)
- The Apache HTTP Server is affected by a man-in-the-middle vulnerability known as 'httpoxy' due to a failure to properly resolve namespace conflicts in accordance with RFC 3875 section 4.1.18. The HTTP_PROXY environment variable is set based on untrusted user data in the 'Proxy' header of HTTP requests. The HTTP_PROXY environment variable is used by some web client libraries to specify a remote proxy server. An unauthenticated, remote attacker can exploit this, via a crafted 'Proxy' header in an HTTP request, to redirect an application's internal HTTP traffic to an arbitrary proxy server where it may be observed or manipulated. (CVE-2016-5387)
- A denial of service vulnerability exists in the mod_http2 module due to improper handling of the LimitRequestFields directive. An unauthenticated, remote attacker can exploit this, via specially crafted CONTINUATION frames in an HTTP/2 request, to inject unlimited request headers into the server, resulting in the exhaustion of memory resources. (CVE-2016-8740)
- A flaw exists due to improper handling of whitespace patterns in user-agent headers. An unauthenticated, remote attacker can exploit this, via a specially crafted user-agent header, to cause the program to incorrectly process sequences of requests, resulting in interpreting responses incorrectly, polluting the cache, or disclosing the content from one request to a second downstream user-agent. (CVE-2016-8743)
- A CRLF vulnerability exists in the mod_userdir module. An unauthenticated, remote attacker can exploit this, allowing HTTP response splitting attacks. (CVE-2016-4975)
Note that the scanner has not tested for these issues but has instead relied only on the application's self-reported version number.
SolutionUpgrade to Apache version 2.4.25 or later. Note that the 'httpoxy' vulnerability can be mitigated by applying the workarounds or patches as referenced in the vendor advisory asf-httpoxy-response.txt. Furthermore, to mitigate the other vulnerabilities, ensure that the affected modules (mod_session_crypto, mod_auth_digest, and mod_http2) are not in use.