__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ ADVISORY NOTICE Apache/mod_ssl Worm [CERTŪ Advisory CA-2002-27] September 16, 2002 17:00 GMT Number M-125 ______________________________________________________________________________ PROBLEM: There have been numerous reports of self-propagating malicious code which exploits a vulnerability (VU#102795) in OpenSSL. PLATFORM: Linux systems running Apache with the OpenSSL module (mod_ssl) on Intel architectures, versions prior to 0.9.6e. DAMAGE: Exploiting this vulnerability can lead to a compromise at the apache user level. This worm also has the capabilities to initiate DDoS attacks using infected systems. SOLUTION: Upgrade to OpenSSL version 0.9.6e or higher, or apply available patches. ______________________________________________________________________________ VULNERABILITY The risk is HIGH. This worm is in the wild. CIAC has received ASSESSMENT: reports of infected and compromised systems. Not only can exploited systems be used to gain access but they can also be used for distributed denial of service (DDoS) attacks. ______________________________________________________________________________ LINKS: CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/m-125.shtml ORIGINAL BULLETIN: http://www.cert.org/advisories/CA-2002-27.html PATCHES: http://www.openssl.org/news/patch_20020730_0_9_6d.txt http://www.openssl.org/news/patch_20020730_0_9_7.txt ______________________________________________________________________________ [***** Start CERT Advisory CA-2002-27 *****] CERTŪ Advisory CA-2002-27 Apache/mod_ssl Worm Original release date: September 14, 2002 Last revised: September 16, 2002 11:19 EDT (UTC-0500) Source: CERT/CC A complete revision history can be found at the end of this file. Systems Affected Linux systems running Apache with mod_ssl accessing SSLv2-enabled OpenSSL 0.9.6d or earlier on Intel x86 architectures Overview The CERT/CC has received reports of self-propagating malicious code which exploits a vulnerability (VU#102795) in OpenSSL. This malicious code has been referred to as Apache/mod_ssl worm, linux.slapper.worm and bugtraq.c worm. Reports received by the CERT/CC indicate that the Apache/mod_ssl worm has already infected thousands of systems. I. Description The Apache/mod_ssl worm is self-propagating malicious code that exploits the OpenSSL vulnerability described in VU#102795. This vulnerability was the among the topics discussed in CA-2002-23 Multiple Vulnerabilities In OpenSSL. While this OpenSSL server vulnerability exists on a wide variety of platforms, the Apache/mod_ssl worm appears to work only on Linux systems running Apache with the OpenSSL module (mod_ssl) on Intel architectures. The Apache/mod_ssl worm scans for potentially vulnerable systems on 80/tcp using an invalid HTTP GET request. GET /mod_ssl:error:HTTP-request HTTP/1.0 When an Apache system is detected, it attempts to send exploit code to the SSL service via 443/tcp. If successful, a copy of the malicious source code is then placed on the victim server, where the attacking system tries to compile and run it. Once infected, the victim server begins scanning for additional hosts to continue the worm's propagation. Additionally, the Apache/mod_ssl worm can act as an attack platform for distributed denial-of-service (DDoS) attacks against other sites by building a network of infected hosts. During the infection process, the attacking host instructs the newly-infected victim to initiate traffic on 2002/udp back to the attacker. Once this communications channel has been established, the infected system becomes part of the Apache/mod_ssl worm's DDoS network. Infected hosts can then share information on other infected systems as well as attack instructions. Thus, the 2002/udp traffic can be used by a remote attacker as a communications channel between infected systems to coordinate attacks on other sites. Reports to the CERT/CC indicate that the high volume of 2002/udp traffic generated between hosts infected with the Apache/mod_ssl worm may itself lead to performance issues on networks with infected hosts. Furthermore, since repairing an infected host does not remove its IP address from the Apache/mod_ssl worm's Peer-to-Peer network, sites that have had hosts infected with the Apache/mod_ssl worm and subsequently patched them may continue to see significant levels of 2002/udp traffic directed at those formerly infected systems. Identifying infected hosts Reports indicate that the Apache/mod_ssl worm's source code is placed in /tmp/.bugtraq.c on infected systems. It is compiled with gcc, resulting in the executable binary being stored at /tmp/.bugtraq; therefore, presence of any of the following files on Linux systems running Apache with OpenSSL is indicative of compromise. /tmp/.bugtraq.c /tmp/.bugtraq The probing phase of the attack may show up in web server logs as shown in the example below. Actual log entries may vary from system to system, but will generally include an "SSL handshake failed" followed by an OpenSSL library error. It is important to note that there may be other causes of such log entries, so the appearance of entries matching (or similar to) these in a web server log should not be construed as evidence of compromise. Rather, their presence is indicative that further investigation may be warranted. For example, : GET /mod_ssl:error:HTTP-request HTTP/1.0 Reports received by the CERT/CC indicate that Apache systems may subsequently log messages similar to the following: [error] SSL handshake failed: HTTP spoken on HTTPS port; trying to send HTML error page (OpenSSL library error follows) [error] OpenSSL: error:1407609C:SSL routines:SSL23_GET_CLIENT_HELLO:http request [Hint: speaking HTTP to HTTPS port!?] Hosts found to be listening for or transmitting data on 2002/udp are also indicative of compromise by the Apache/mod_ssl worm. Detecting Apache/mod_ssl worm activity on the network Infected systems are readily identifiable on a network by the following traffic characteristics: Probing -- Scanning on 80/tcp Propagation -- Connections to 443/tcp DDoS -- Transmitting or receiving datagrams with both source and destination ports 2002/udp. This traffic is used as a communications channel between infected systems to coordinate attacks on other sites. Additionally, infected hosts that are actively participating in DDoS attacks against other systems may generate unusually high volumes of attack traffic using various protocols (e.g., TCP, UDP, ICMP) II. Impact Compromise by the Apache/mod_ssl worm indicates that a remote attacker can execute arbitrary code as the apache user on the victim system. It may be possible for an attacker to subsequently leverage a local privilege escalation exploit in order to gain root access to the victim system. The high volume of 2002/udp traffic generated between hosts infected with the Apache/mod_ssl worm may itself lead to performance issues on networks with infected or formerly infected hosts. Furthermore, the DDoS capabilities included in the Apache/mod_ssl worm allow victim systems to be used as platforms to attack other systems. III. Solution Apply a patch Administrators of all systems running OpenSSL are encouraged to review CA-2002-23 and VU#102795 for detailed vendor recommendations regarding patches. Note that while the vulnerability exploited by the Apache/mod_ssl worm was fixed beginning with OpenSSL version 0.9.6e, as of this writing the latest version of OpenSSL is 0.9.6g. Administrators may wish to upgrade to that version instead. The following is reproduced in part from CA-2002-23 Upgrade to version 0.9.6e of OpenSSL Upgrade to version 0.9.6e of OpenSSL to resolve the issues addressed in this advisory. As noted in the OpenSSL advisory, separate patches are available: Combined patches for OpenSSL 0.9.6d: http://www.openssl.org/news/patch_20020730_0_9_6d.txt After either applying the patches above or upgrading to 0.9.6e, recompile all applications using OpenSSL to support SSL or TLS services, and restart said services or systems. This will eliminate all known vulnerable code. Sites running OpenSSL pre-release version 0.9.7-beta2 may wish to upgrade to 0.9.7- beta3, which corrects these vulnerabilities. Separate patches are available as well: Combined patches for OpenSSL 0.9.7 beta 2: http://www.openssl.org/news/patch_20020730_0_9_7.txt Disable SSLv2 Disabling SSLv2 handshaking will prevent exploitation of VU#102795. CERT/CC recomends consulting the mod_ssl documentation for a complete description of the options but one method for disabling SSLv2 is to remove SSLv2 as a supported cipher in the SSLCipherSuite directive in the configuration file. For example: SSLCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+SSLv2 which allows SSLv2 can be changed to SSLCipherSuite ALL:!ADH:RC4+RSA:+HIGH:!SSLv2 which will disable SSLv2. Note the changing of +SSLv2 to !SSLv2. However, systems may still be susceptible to the other vulnerabilities described in CA- 2002-23. Ingress/Egress filtering The following steps are only effective in limiting the damage that systems already infected with the Apache/mod_ssl worm can do. They provide no protection whatsoever against the initial infection of systems. As a result, these steps are only recommended in addition to the preventative steps outlined above, not in lieu thereof. Ingress filtering manages the flow of traffic as it enters a network under your administrative control. Servers are typically the only machines that need to accept inbound traffic from the public Internet. In the network usage policy of many sites, external hosts are only permitted to initiate inbound traffic to machines that provide public services on specific ports. Thus, ingress filtering should be performed at the border to prohibit externally initiated inbound traffic to non-authorized services. Egress filtering manages the flow of traffic as it leaves a network under your administrative control. There is typically limited need for machines providing public services to initiate outbound connections to the Internet. In the case of the Apache/mod_ssl worm, employing ingress and egress filtering can help prevent systems on your network from participating in the worm's DDoS network and attacking systems elsewhere. Blocking UDP datagrams with both source and destination port 2002 from entering or leaving your network reduces the risk of external infected systems communicating with infected hosts inside your network. Recovering from a system compromise If you believe a system under your administrative control has been compromised, please follow the steps outlined in Steps for Recovering from a UNIX or NT System Compromise Reporting The CERT/CC is interested in receiving reports of this activity. If machines under your administrative control are compromised, please send mail to cert@cert.org with the following text included in the subject line: "[CERT#23820]". [ DOE sites should report any activity to ciac@ciac.org ] -------------------------------------------------------------------------------- Feedback can be directed to the author: Allen Householder -------------------------------------------------------------------------------- This document is available from: http://www.cert.org/advisories/CA-2002-27.html [***** End CERT Advisory CA-2002-27 *****] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of CERT for the information contained in this bulletin. _______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be contacted at: Voice: +1 925-422-8193 (7x24) FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@ciac.org Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://www.ciac.org/ Anonymous FTP: ftp.ciac.org PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities receive CIAC bulletins. If you are not part of these communities, please contact your agency's response team to report incidents. Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC) M-116: Microsoft Cumulative Patch for Internet Explorer M-117: Microsoft Office Web Components Vulnerabilities M-118: HP Tru64 Unix Multiple Vulnerabilities M-119: Cisco VPN 3000 Concentrator Multiple Vulnerabilities M-120: Microsoft Visual FoxPro 6.0 Vulnerability M-121: Microsoft Certificate Validation Vulnerability M-122: Remotely Exploitable Buffer Overflow in PGP M-123: Polycom Videoconferencing Remote Vulnerabilities M-124: Konqueror Secure Cookie Vulnerability