CVE-2017-17439 — In Heimdal through 7

In Heimdal through 7.4, remote unauthenticated attackers are able to crash the KDC by sending a crafted UDP packet containing empty data fields for client name or realm. The parser would unconditionally dereference NULL pointers in that case, leading to a segmentation fault. This

01What is this vulnerability?

In Heimdal through 7.4, remote unauthenticated attackers are able to crash the KDC by sending a crafted UDP packet containing empty data fields for client name or realm. The parser would unconditionally dereference NULL pointers in that case, leading to a segmentation fault. This is related to the _kdc_as_rep function in kdc/kerberos5.c and the der_length_visible_string function in…

02Affected products

No structured affected-product list available — see references below for vendor advisories.

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: 2017-12-06T15:29:00.250
• Last modified: 2026-05-13T00:24:29.033

09References

• h5l.org — http://h5l.org/advisories.html?show=2017-12-08
• www.h5l.org — http://www.h5l.org/pipermail/heimdal-announce/2017-December/000008.html
• www.h5l.org — http://www.h5l.org/pipermail/heimdal-discuss/2017-August/000259.html
• bugs.debian.org — https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=878144
• github.com — https://github.com/heimdal/heimdal/commit/1a6a6e462dc2ac6111f9e02c6852ddec4849b8…
• github.com — https://github.com/heimdal/heimdal/issues/353
• www.debian.org — https://www.debian.org/security/2017/dsa-4055
• h5l.org — http://h5l.org/advisories.html?show=2017-12-08
• www.h5l.org — http://www.h5l.org/pipermail/heimdal-announce/2017-December/000008.html
• www.h5l.org — http://www.h5l.org/pipermail/heimdal-discuss/2017-August/000259.html