What is CVE-2021-27804?

CVE-2021-27804 is a critical-severity vulnerability in Libjxl Project, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2021-03-02.

How severe is CVE-2021-27804?

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

Buffer overflow in Libjxl Project

CVE-2021-27804

JPEG XL (aka jpeg-xl) through 0.3.2 allows writable memory corruption.

Vulnerability class: Buffer Overflow

Published 2021-03-02 · 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: 0.040 (90.2th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 90th percentile — 90.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.040 · newest: 0.040 · change: 0.000

Affected products

Libjxl Project

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

References

gitlab.com/wg1/jpeg-xl/-/tags (Third Party Advisory)
www.openwall.com/lists/oss-security/2021/03/01/3 (Mailing List, Third Party Advisory)
seclists.org/fulldisclosure/2021/Mar/2 (mailing-list, Third Party Advisory)
packetstormsecurity.com/files/161623/jpeg-xl-0.3.1-Memory-Corruption.html (Third Party Advisory)

Frequently asked questions

What is CVE-2021-27804?: CVE-2021-27804 is a critical-severity vulnerability in Libjxl Project, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2021-03-02.
How severe is CVE-2021-27804?: Critical severity. CVSS v3 base score is 9.8 out of 10.