CVE-2018-21029

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 3.1% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2019-10-30 · updated 2026-06-17
Weakness: CWE-295

Description

systemd 239 through 245 accepts any certificate signed by a trusted certificate authority for DNS Over TLS. Server Name Indication (SNI) is not sent, and there is no hostname validation with the GnuTLS backend. NOTE: This has been disputed by the developer as not a vulnerability since hostname validation does not have anything to do with this issue (i.e. there is no hostname to be sent)

Affected products

Fedoraproject Fedora: 31
systemd: from 239 before 244 — fixed in 244

How to fix

Upgrade to a fixed version: systemd 244. Check the vendor advisory for mitigations.

References

https://blog.cloudflare.com/dns-encryption-explained/
https://github.com/systemd/systemd/blob/v239/man/resolved.conf.xml#L199-L207
https://github.com/systemd/systemd/blob/v243/man/resolved.conf.xml#L196-L207
https://github.com/systemd/systemd/blob/v243/src/resolve/resolved-dnstls-gnutls.c#L62-L63
https://github.com/systemd/systemd/issues/9397
https://github.com/systemd/systemd/pull/13870
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4NLJVOJMB6ANDILRLDZK26YGLYBEPHKY/
https://security.netapp.com/advisory/ntap-20191122-0002/
https://tools.ietf.org/html/rfc7858#section-4.1
https://blog.cloudflare.com/dns-encryption-explained/
https://github.com/systemd/systemd/blob/v239/man/resolved.conf.xml#L199-L207
https://github.com/systemd/systemd/blob/v243/man/resolved.conf.xml#L196-L207

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