Bug 1889688 (CVE-2020-25685)
| Summary: | CVE-2020-25685 dnsmasq: loose query name check in reply_query() makes forging replies easier for an off-path attacker | ||
|---|---|---|---|
| Product: | [Other] Security Response | Reporter: | Riccardo Schirone <rschiron> |
| Component: | vulnerability | Assignee: | Red Hat Product Security <security-response-team> |
| Status: | CLOSED ERRATA | QA Contact: | |
| Severity: | medium | Docs Contact: | |
| Priority: | medium | ||
| Version: | unspecified | CC: | aegorenk, code, dbecker, dblechte, dfediuck, dns-sig, dougsland, eedri, emarcus, itamar, jima, jjoyce, jschluet, jsvoboda, laine, lhh, lpeer, mburns, mgoldboi, michal.skrivanek, nlevy, pemensik, sbonazzo, sclewis, security-response-team, sherold, slinaber, veillard, yturgema |
| Target Milestone: | --- | Keywords: | Patch, Security |
| Target Release: | --- | ||
| Hardware: | All | ||
| OS: | Linux | ||
| Whiteboard: | |||
| Fixed In Version: | dnsmasq 2.83 | Doc Type: | Known Issue |
| Doc Text: |
A flaw was found in dnsmasq. When getting a reply from a forwarded query, dnsmasq checks in forward.c:reply_query(), which is the forwarded query that matches the reply, by only using a weak hash of the query name. Due to the weak hash (CRC32 when dnsmasq is compiled without DNSSEC, SHA-1 when it is) this flaw allows an off-path attacker to find several different domains all having the same hash, substantially reducing the number of attempts they would have to perform to forge a reply and get it accepted by dnsmasq. This is in contrast with RFC5452, which specifies that the query name is one of the attributes of a query that must be used to match a reply. This flaw could be abused to perform a DNS Cache Poisoning attack. If chained with CVE-2020-25684 the attack complexity of a successful attack is reduced. The highest threat from this vulnerability is to data integrity.
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Story Points: | --- |
| Clone Of: | Environment: | ||
| Last Closed: | 2021-01-19 17:59:24 UTC | Type: | --- |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
| Bug Depends On: | 1896056, 1896058, 1896060, 1896062, 1896065, 1896067, 1896069, 1896071, 1917318, 1917319, 1917761, 1917785, 1917792, 1918953, 1918954 | ||
| Bug Blocks: | 1875522 | ||
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Description
Riccardo Schirone
2020-10-20 11:30:11 UTC
Red Hat Enterprise Linux 5, 6, and 7 are all affected in the same way and the same mitigations apply. Red Hat Enterprise Linux 8 provides dnsmasq compiled with DNSSEC, thus SHA-1 is used as hash for query names instead of CRC32. This makes it slightly harder to find collisions in this case. The same mitigations apply anyway. Mitigation: The impact of this flaw can be reduced by disabling the dnsmasq cache by adding `--cache-size=0` when calling dnsmasq or by adding a line with `cache-size=0` to the dnsmasq configuration file (/etc/dnsmasq.conf by default). When using Red Hat Enterprise Linux 8.3 with libvirt through a virt:rhel module, use `virsh net-edit <network-name>` and reference https://libvirt.org/formatnetwork.html#elementsNamespaces to add the suggested option `cache-size=0`. There is no way to customize the dnsmasq configuration generated by libvirt, when using versions of Red Hat Enterprise Linux prior to version 8.3. If dnsmasq is being run through NetworkManager, create a new file in /etc/NetworkManager/dnsmasq.d/ and add `cache-size=0` to it. In all cases, by disabling the cache, you may experience a performance loss in your environment due to all DNS queries being forwarded to the upstream servers. Please evaluate if the mitigation is appropriate for the system’s environment before applying. Statement: Dnsmasq may be run by libvirt and/or NetworkManager. libvirt uses dnsmasq by default to provide DNS service to its guests. NetworkManager may be configured to use dnsmasq to provide DNS service to the system, if a line `dns=dnsmasq` is present in the `[main]` section of the configuration file /etc/NetworkManager/NetworkManager.conf. In Red Hat OpenStack Platform (RHOSP) and Red Hat Virtualization (RHV), the dnsmasq package is provided by the underlying Red Hat Enterprise Linux (RHEL) product. RHOSP and RHV are therefore indirectly affected, so please ensure that the underlying RHEL dnsmasq package is updated. Acknowledgments: Name: Moshe Kol (JSOF), Shlomi Oberman (JSOF) External References: https://www.jsof-tech.com/disclosures/dnspooq/ Created dnsmasq tracking bugs for this issue: Affects: fedora-all [bug 1917785] This issue has been addressed in the following products: Red Hat Enterprise Linux 8.1 Extended Update Support Via RHSA-2021:0152 https://access.redhat.com/errata/RHSA-2021:0152 This issue has been addressed in the following products: Red Hat Enterprise Linux 8 Via RHSA-2021:0150 https://access.redhat.com/errata/RHSA-2021:0150 Upstream patches: http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=2d765867c597db18be9d876c9c17e2c0fe1953cd http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=2024f9729713fd657d65e64c2e4e471baa0a3e5b This issue has been addressed in the following products: Red Hat Enterprise Linux 8.2 Extended Update Support Via RHSA-2021:0151 https://access.redhat.com/errata/RHSA-2021:0151 This issue has been addressed in the following products: Red Hat Enterprise Linux 7.4 Advanced Update Support Red Hat Enterprise Linux 7.4 Update Services for SAP Solutions Red Hat Enterprise Linux 7.4 Telco Extended Update Support Via RHSA-2021:0156 https://access.redhat.com/errata/RHSA-2021:0156 This issue has been addressed in the following products: Red Hat Enterprise Linux 7 Via RHSA-2021:0153 https://access.redhat.com/errata/RHSA-2021:0153 This issue has been addressed in the following products: Red Hat Enterprise Linux 7.7 Extended Update Support Via RHSA-2021:0154 https://access.redhat.com/errata/RHSA-2021:0154 This issue has been addressed in the following products: Red Hat Enterprise Linux 7.6 Extended Update Support Via RHSA-2021:0155 https://access.redhat.com/errata/RHSA-2021:0155 This bug is now closed. Further updates for individual products will be reflected on the CVE page(s): https://access.redhat.com/security/cve/cve-2020-25685 This issue has been addressed in the following products: Red Hat Enterprise Linux 7.2 Advanced Update Support Via RHSA-2021:0240 https://access.redhat.com/errata/RHSA-2021:0240 This issue has been addressed in the following products: Red Hat Enterprise Linux 7.3 Advanced Update Support Via RHSA-2021:0245 https://access.redhat.com/errata/RHSA-2021:0245 This issue has been addressed in the following products: Red Hat Virtualization 4 for Red Hat Enterprise Linux 7 Via RHSA-2021:0395 https://access.redhat.com/errata/RHSA-2021:0395 This issue has been addressed in the following products: Red Hat Virtualization 4 for Red Hat Enterprise Linux 8 Via RHSA-2021:0401 https://access.redhat.com/errata/RHSA-2021:0401 |