CVE-2020-8617 — bind9
MEDIUMCVE-2020-8617 is a medium-severity (CVSS 5.9) Reachable Assertion vulnerability. 4 public exploit references exist, so weaponization risk is real. No vendor fix is recorded yet; mitigation options are listed below.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2020-8617 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 395,249 CVEs with a current EPSS score, this one falls in the ≥ 90% band (highlighted). Counts from FIRST.org, log-scaled.
Description
Using a specially-crafted message, an attacker may potentially cause a BIND server to reach an inconsistent state if the attacker knows (or successfully guesses) the name of a TSIG key used by the server. Since BIND, by default, configures a local session key even on servers whose configuration does not otherwise make use of it, almost all current BIND servers are vulnerable. In releases of BIND dating from March 2018 and after, an assertion check in tsig.c detects this inconsistent state and deliberately exits. Prior to the introduction of the check the server would continue operating in an inconsistent state, with potentially harmful results.
Affected Products
ubuntu linuxcanonicaldebian linuxdebianfedorafedoraprojectbindiscleapopensuseResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
BIND - 'TSIG' Denial of Service
by Teppei Fukuda · May 20, 2020
Detection & mitigation playbook
VulnerabilityDetect
Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).
Remediation status
No fixed release is recorded for CVE-2020-8617 yet. Track the upstream advisory, and apply the exposure-reduction steps below in the meantime.
Mitigate without a patch
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Upstream has released additional information about this flaw. Details available at: https://kb.isc.org/docs/cve-2020-8617-faq-and-supplemental-information
BIND servers have an internally-generated TSIG session key whose name is trivially guessable, and that key exposes the vulnerability unless specifically disabled. Upstream recommends using random value in session-keyname as a workaround. This can be added to named.conf configuration file.Source: Red Hat security advisory for CVE-2020-8617 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 6 | bind-32:9.8.2-0.68.rc1.el6_10.7 | RHSA-2020:2383 |
| Red Hat Enterprise Linux 6.5 Advanced Update Support | bind-32:9.8.2-0.23.rc1.el6_5.9 | RHSA-2020:3379 |
| Red Hat Enterprise Linux 6.6 Advanced Update Support | bind-32:9.8.2-0.30.rc1.el6_6.11 | RHSA-2020:3378 |
| Red Hat Enterprise Linux 7 | bind-32:9.11.4-16.P2.el7_8.6 | RHSA-2020:2344 |
| Red Hat Enterprise Linux 7.2 Advanced Update Support | bind-32:9.9.4-29.el7_2.9 | RHSA-2020:3471 |
| Red Hat Enterprise Linux 7.3 Advanced Update Support | bind-32:9.9.4-50.el7_3.4 | RHSA-2020:3470 |
| Red Hat Enterprise Linux 7.4 Advanced Update Support | bind-32:9.9.4-51.el7_4.4 | RHSA-2020:3433 |
| Red Hat Enterprise Linux 7.6 Extended Update Support | bind-32:9.9.4-74.el7_6.4 | RHSA-2020:3475 |
Frequently Asked Questions
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