CVE-2019-8460 — OpenBSD kernel version <= 6

OpenBSD kernel version <= 6.5 can be forced to create long chains of TCP SACK holes that causes very expensive calls to tcp_sack_option() for every incoming SACK packet which can lead to a denial of service.

01What is this vulnerability?

OpenBSD kernel version <= 6.5 can be forced to create long chains of TCP SACK holes that causes very expensive calls to tcp_sack_option() for every incoming SACK packet which can lead to a denial of service.

02Affected products

Vendor	Product	Versions
n	a / OpenBSD	All, including latest - 6.5

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: 2019-08-26T19:18:49.000Z
• Last modified: 2024-08-04T21:17:31.425Z

09References

• github.com — https://github.com/openbsd/src/commit/ed8fdce754a5d8d14c09e989d8877707bd43906f
• ftp.openbsd.org — https://ftp.openbsd.org/pub/OpenBSD/patches/6.5/common/006_tcpsack.patch.sig
• security.netapp.com — https://security.netapp.com/advisory/ntap-20190905-0001/
• research.checkpoint.com — https://research.checkpoint.com/tcp-sack-security-issue-in-openbsd-cve-2019-8460…
• us-cert.cisa.gov — https://us-cert.cisa.gov/ics/advisories/icsa-19-253-03