What is CVE-2019-20056?

CVE-2019-20056 is a medium-severity vulnerability in Nothings Stb Image.h, classified under Reachable Assertion. CVSS score: 6.5/10. Published 2019-12-29.

How severe is CVE-2019-20056?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Nothings Stb Image.h

CVE-2019-20056

stb_image.h (aka the stb image loader) 2.23, as used in libsixel and other products, has an assertion failure in stbi__shiftsigned.

Published 2019-12-29 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.009 (59.2th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 59th percentile — 59.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000

Affected products

Nothings Stb Image.h — versions 2.23

Weakness classification (CWE)

CWE-617 — Reachable Assertion

References

github.com/saitoha/libsixel/issues/126 (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2019-20056?: CVE-2019-20056 is a medium-severity vulnerability in Nothings Stb Image.h, classified under Reachable Assertion. CVSS score: 6.5/10. Published 2019-12-29.
How severe is CVE-2019-20056?: Medium severity. CVSS v3 base score is 6.5 out of 10.