What is CVE-2018-20721?

CVE-2018-20721 is a critical-severity vulnerability in Uriparser Project, classified under Out-of-bounds Read. CVSS score: 9.8/10. Published 2019-01-16.

How severe is CVE-2018-20721?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Out-of-bounds Read in Uriparser Project

CVE-2018-20721

URI_FUNC() in UriParse.c in uriparser before 0.9.1 has an out-of-bounds read (in uriParse*Ex* functions) for an incomplete URI with an IPv6 address containing an embedded IPv4 address, such as a "//[::44.1" address.

Vulnerability class: Buffer Overflow

Published 2019-01-16 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.021 (80.9th percentile), scored 2026-10-19.

Low probability of exploitation in the next 30 days, but still tracked. 81st percentile — 80.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.021 · newest: 0.021 · change: 0.000

Affected products

Uriparser Project
Debian Linux — versions 8.0, 9.0

Weakness classification (CWE)

CWE-125 — Out-of-bounds Read

References

lists.debian.org/debian-lts-announce/2019/02/msg00028.html (mailing-list, Mailing List, Third Party Advisory)
github.com/uriparser/uriparser/commit/cef25028de5ff872c2e1f0a6c562eb3ea9ecbce4 (Patch, Third Party Advisory)
github.com/uriparser/uriparser/blob/master/ChangeLog (Third Party Advisory, Release Notes)
lists.debian.org/debian-lts-announce/2021/11/msg00029.html (mailing-list, Mailing List, Third Party Advisory)

Frequently asked questions

What is CVE-2018-20721?: CVE-2018-20721 is a critical-severity vulnerability in Uriparser Project, classified under Out-of-bounds Read. CVSS score: 9.8/10. Published 2019-01-16.
How severe is CVE-2018-20721?: Critical severity. CVSS v3 base score is 9.8 out of 10.