CVE-2018-21029 — systemd 239 through 245 accepts any certificate signed by a trusted certificate

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

01What is this vulnerability?

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)

02Affected products

Vendor	Product	Versions
n	a / n/a	n/a

03Active exploitation status

Not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog. EPSS is the best forward-looking signal — see the EPSS row above.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Ask SARA in chat to draft a starting detection for this CVE in your stack of choice.

07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2019-10-30T21:46:51.000Z
• Last modified: 2024-08-05T12:19:27.514Z

09References

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