CVE-2018-15473 is a medium-severity (CVSS 5.3) CWE-362 vulnerability. 26 public exploit references exist, so weaponization risk is real. A fix is available — see the affected versions and patch details below.
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2018-15473.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2018-15473 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,803 CVEs with a current EPSS score, this one falls in the ≥ 90% band (highlighted). Counts from FIRST.org, log-scaled.
Description
OpenSSH through 7.7 is prone to a user enumeration vulnerability due to not delaying bailout for an invalid authenticating user until after the packet containing the request has been fully parsed, related to auth2-gss.c, auth2-hostbased.c, and auth2-pubkey.c.
Affected Products
ubuntu linuxcanonicaldebian linuxdebianaff baseboard management controllernetappcloud backupnetappclustered data ontapnetappcn1610 firmwarenetappResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
OpenSSH 2.3 < 7.7 - Username Enumeration
by Justin Gardner · Aug 21, 2018
OpenSSH 2.3 < 7.7 - Username Enumeration (PoC)
by Matthew Daley · Aug 16, 2018
OpenSSH < 7.7 - User Enumeration (2)
by Leap Security · Dec 4, 2018
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`).
Fix
Upgrade the affected component to the fixed release for CVE-2018-15473, or apply your distribution's backported patch — distro builds are often patched at an older version number, so check your vendor's advisory rather than the upstream version alone.
Workarounds
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.
Red Hat Product Security has rated this issue as having Low severity. An attacker could use this flaw to determine whether given usernames exist or not on the server, but no further information is disclosed and there is no availability or integrity impact. A future update may address this issue.
Configuring your firewall to limit the origin and/or rate of incoming ssh connections (using the netfilter xt_recent module) will limit the impact of this attack, as it requires a new TCP connection for each username tested. This configuration also provides some protection against brute-force attacks on SSH passwords or keys. See the following article for more information on limiting access to SSHD: https://access.redhat.com/solutions/8687Source: Red Hat security advisory for CVE-2018-15473 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 6 | openssh-0:5.3p1-124.el6_10 | RHSA-2019:0711 |
| Red Hat Enterprise Linux 7 | openssh-0:7.4p1-21.el7 | RHSA-2019:2143 |
Frequently Asked Questions
Is CVE-2018-15473 in your dependencies?
Find it across , including transitive dependencies.