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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2021.0227 ICS Advisory (ICSA-21-019-01) - dnsmasq vulnerabilities 20 January 2021 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: dnsmasq Publisher: ICS-CERT Operating System: UNIX variants (UNIX, Linux, OSX) Impact/Access: Execute Arbitrary Code/Commands -- Remote/Unauthenticated Denial of Service -- Remote/Unauthenticated Provide Misleading Information -- Remote/Unauthenticated Reduced Security -- Remote/Unauthenticated Resolution: Patch/Upgrade CVE Names: CVE-2020-25687 CVE-2020-25686 CVE-2020-25685 CVE-2020-25684 CVE-2020-25683 CVE-2020-25682 CVE-2020-25681 Reference: ESB-2021.0219 ESB-2021.0218 ESB-2021.0217 Original Bulletin: https://us-cert.cisa.gov/ics/advisories/icsa-21-019-01 - --------------------------BEGIN INCLUDED TEXT-------------------- ICS Advisory (ICSA-21-019-01) Dnsmasq by Simon Kelley Original release date: January 19, 2021 Legal Notice All information products included in https://us-cert.cisa.gov/ics are provided "as is" for informational purposes only. The Department of Homeland Security (DHS) does not provide any warranties of any kind regarding any information contained within. DHS does not endorse any commercial product or service, referenced in this product or otherwise. Further dissemination of this product is governed by the Traffic Light Protocol (TLP) marking in the header. For more information about TLP, see https://us-cert.cisa.gov/tlp/ . 1. EXECUTIVE SUMMARY o CVSS v3 8.1 o ATTENTION: Exploitable remotely/low skill level to exploit o Vendor: Dnsmasq by Simon Kelley o Equipment: Dnsmasq o Vulnerabilities: Heap-based Buffer Overflow, Insufficient Verification of Data Authenticity, Use of a Broken or Risky Cryptographic Algorithm CISA is aware of a public report, known as "DNSpooq" that details vulnerabilities found in Dnsmasq, a prevalent lightweight DNS and DHCP server developed and maintained by Simon Kelley. CISA is issuing this advisory to provide early notice of the reported vulnerabilities and identify baseline mitigations for reducing risks to these and other cybersecurity attacks. 2. RISK EVALUATION Successful exploitation of these vulnerabilities could result in cache poisoning, remote code execution, and a denial-of-service condition. 3. TECHNICAL DETAILS 3.1 AFFECTED PRODUCTS The following versions of Dnsmasq DNS and DHCP server are affected: o Version 2.8.2 and prior 3.2 VULNERABILITY OVERVIEW 3.2.1 HEAP-BASED BUFFER OVERFLOW CWE-122 A heap-based buffer overflow was discovered in Dnsmasq in the way it sorts RRSets before validating them with DNSSEC data. An attacker on the network could forge DNS replies to be accepted as valid to cause an overflow with arbitrary data in a heap-allocated memory, resulting in code execution. CVE-2020-25681 has been assigned to this vulnerability. A CVSS v3 base score of 8.1 has been calculated; the CVSS vector string is ( AV:N/AC:H/PR:N/UI:N/S:U/ C:H/I:H/A:H ). 3.2.2 HEAP-BASED BUFFER OVERFLOW CWE-122 A buffer overflow vulnerability was discovered in the way Dnsmasq extracts names from DNS packets before validating them with DNSSEC data. An attacker on the network could create valid DNS replies to cause an overflow with arbitrary data in a heap-allocated memory, resulting in code execution. CVE-2020-25682 has been assigned to this vulnerability. A CVSS v3 base score of 8.1 has been calculated; the CVSS vector string is ( AV:N/AC:H/PR:N/UI:N/S:U/ C:H/I:H/A:H ). 3.2.3 HEAP-BASED BUFFER OVERFLOW CWE-122 A heap-based buffer overflow was discovered in Dnsmasq when DNSSEC is enabled and before it validates the received DNS entries. A remote attacker could create valid DNS replies to cause an overflow in a heap-allocated memory and cause a crash in Dnsmasq, resulting in a denial-of-service condition. CVE-2020-25683 has been assigned to this vulnerability. A CVSS v3 base score of 5.9 has been calculated; the CVSS vector string is ( AV:N/AC:H/PR:N/UI:N/S:U/ C:N/I:N/A:H ). 3.2.4 INSUFFICIENT VERIFICATION OF DATA AUTHENTICITY CWE-345 A vulnerability exists when getting a reply from a forwarded query, where Dnsmasq checks in forward.c:reply_query() if the reply destination address/port is used by the pending forwarded queries. This could allow an attacker to perform a DNS cache poisoning attack. CVE-2020-25684 has been assigned to this vulnerability. A CVSS v3 base score of 4.0 has been calculated; the CVSS vector string is ( AV:N/AC:H/PR:N/UI:N/S:C/ C:N/I:L/A:N ). 3.2.5 USE OF A BROKEN OR RISKY CRYPTOGRAPHIC ALGORITHM CWE-327 Due to a weak hash, an off-path attacker can find several different domains with the same hash, substantially reducing the number of attempts to forge a reply for acceptance by Dnsmasq. This could allow an attacker to perform a DNS cache poisoning attack. CVE-2020-25685 has been assigned to this vulnerability. A CVSS v3 base score of 4.0 has been calculated; the CVSS vector string is ( AV:N/AC:H/PR:N/UI:N/S:C/ C:N/I:L/A:N ). 3.2.6 INSUFFICIENT VERIFICATION OF DATA AUTHENTICITY CWE-345 A flaw was found when receiving a query, where Dnsmasq does not check for an existing pending request for the same name and forwards a new request. This could allow an off-path attacker on the network to substantially reduce the number of attempts to forge a reply and have it accepted by Dnsmasq. CVE-2020-25686 has been assigned to this vulnerability. A CVSS v3 base score of 4.0 has been calculated; the CVSS vector string is ( AV:N/AC:H/PR:N/UI:N/S:C/ C:N/I:L/A:N ). 3.2.7 HEAP-BASED BUFFER OVERFLOW CWE-122 A heap-based buffer overflow was discovered in Dnsmasq when DNSSEC is enabled and before it validates the received DNS entries. A remote attacker could create valid DNS replies and cause an overflow in heap-allocated memory, resulting in a denial-of-service condition. CVE-2020-25687 has been assigned to this vulnerability. A CVSS v3 base score of 5.9 has been calculated; the CVSS vector string is ( AV:N/AC:H/PR:N/UI:N/S:U/ C:N/I:N/A:H ). 3.3 BACKGROUND o CRITICAL INFRASTRUCTURE SECTORS: Multiple o COUNTRIES/AREAS DEPLOYED: Worldwide o COMPANY HEADQUARTERS LOCATION: United Kingdom 3.4 RESEARCHER Moshe Kol and Shlomi Oberman of JSOF reported these vulnerabilities to CISA. 4. MITIGATIONS The maintainers of Dnsmasq recommend users update to the latest version (2.83 or later) The researcher has recommended the following mitigations and workarounds: o Implement Layer 2 security features such as DHCP snooping and IP source guard. o Configure Dnsmasq not to listen to WAN interfaces if unnecessary. o Reduce the maximum queries allowed to be forwarded with the option --dns-forward-max=<queries>. The default is 150, but it could be lowered. o Temporarily disable DNSSEC validation option until you patch. o Use DNS-over-HTTPS or DNS-over-TLS to connect to upstream server. CISA recommends users take defensive measures to minimize the risk of exploitation of this vulnerability. Specifically, users should: o Minimize network exposure for all control system devices and/or systems, and ensure that they are not accessible from the Internet . o Locate control system networks and remote devices behind firewalls, and isolate them from the business network. o When remote access is required, use secure methods, such as Virtual Private Networks (VPNs), recognizing that VPNs may have vulnerabilities and should be updated to the most current version available. Also recognize that VPN is only as secure as the connected devices. CISA reminds organizations to perform proper impact analysis and risk assessment prior to deploying defensive measures. CISA also provides a section for control systems security recommended practices on the ICS webpage on us-cert.cisa.gov . Several recommended practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies . Additional mitigation guidance and recommended practices are publicly available on the ICS webpage on us-cert.cisa.gov in the Technical Information Paper, ICS-TIP-12-146-01B--Targeted Cyber Intrusion Detection and Mitigation Strategies . Organizations observing any suspected malicious activity should follow their established internal procedures and report their findings to CISA for tracking and correlation against other incidents. CISA also recommends users take the following measures to protect themselves from social engineering attacks: o Do not click web links or open unsolicited attachments in email messages. o Refer to Recognizing and Avoiding Email Scams for more information on avoiding email scams. o Refer to Avoiding Social Engineering and Phishing Attacks for more information on social engineering attacks. No known public exploits specifically target these vulnerabilities. For any questions related to this report, please contact the CISA at: Email: CISAservicedesk@cisa.dhs.gov Toll Free: 1-888-282-0870 CISA continuously strives to improve its products and services. You can help by choosing one of the links below to provide feedback about this product. - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. 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It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the author's website to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: https://www.auscert.org.au/bulletins/ =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). 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