What is CVE-2019-11921?

CVE-2019-11921 is a critical-severity vulnerability in Facebook Proxygen, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2019-07-25.

How severe is CVE-2019-11921?

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

Buffer overflow in Facebook Proxygen

CVE-2019-11921

An out of bounds write is possible via a specially crafted packet in certain configurations of Proxygen due to improper handling of Base64 when parsing malformed binary content in Structured HTTP Headers. This issue affects versions of proxygen prior to v2019.07.22.00.

Vulnerability class: Buffer Overflow

Published 2019-07-25 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.021 (81.4th percentile), scored 2026-10-26.

Low probability of exploitation in the next 30 days, but still tracked. 81st percentile — 81.4% 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

Facebook Proxygen — versions v2019.07.22.00, unspecified

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

References

github.com/facebook/proxygen/commit/2f07985bef9fbae124cc63e5c0272e32da4fdaec (Patch, Third Party Advisory)
www.facebook.com/security/advisories/cve-2019-11921 (Third Party Advisory)

Frequently asked questions

What is CVE-2019-11921?: CVE-2019-11921 is a critical-severity vulnerability in Facebook Proxygen, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2019-07-25.
How severe is CVE-2019-11921?: Critical severity. CVSS v3 base score is 9.8 out of 10.