CVE-2021-36978

QPDF 9.x through 9.1.1 and 10.x through 10.0.4 has a heap-based buffer overflow in Pl_ASCII85Decoder::write (called from Pl_AES_PDF::flush and Pl_AES_PDF::finish) when a certain downstream write fails.

Published: 2021-07-20 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-36978 is rated Low Risk (30.2/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.08%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-36978

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2025-11-21 0.25% 0.08% -0.17%
2 2025-11-18 0.08% 0.25% +0.17%
3 2025-03-30 — 0.08% —

Full EPSS history (9 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-36978

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.5 3.1 MEDIUM
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 3.6 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2021-36978

OS Trackers for CVE-2021-36978

vendor priority summary link
debian not yet assigned CVE-2021-36978 not yet assigned priority: Debian including 1 source packages (qpdf), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-36978
gentoo normal CVE-2021-36978: 1 GLSA(s) (202401-20), 1 atom(s) (app-text/qpdf); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-36978
redhat medium — https://access.redhat.com/security/cve/CVE-2021-36978
suse high CVE-2021-36978 severity important: SUSE including 9 source package names (libqpdf18-7.1.1-3.8.1, libqpdf21-8.0.2-150000.3.5.1, …), 96 product×package rows across 43 product lines (SUSE CaaS Platform 4.0, SUSE Enterprise Storage 6, … (43 product lines)): Fixed 96. https://www.suse.com/security/cve/CVE-2021-36978/
ubuntu medium CVE-2021-36978 medium priority: Ubuntu including 1 source packages (qpdf), 8 status rows across 8 suites (bionic, focal, hirsute, impish, jammy, trusty, upstream, xenial): released 4, not-affected 3, DNE 1. https://ubuntu.com/security/CVE-2021-36978

Affected software / configurations for CVE-2021-36978

Vendor Product Version Raw CPE
qpdf_project qpdf >= 9.0.0, <= 9.1.1 cpe:2.3:a:qpdf_project:qpdf:*:*:*:*:*:*:*:*
qpdf_project qpdf >= 10.0.0, <= 10.0.4 cpe:2.3:a:qpdf_project:qpdf:*:*:*:*:*:*:*:*

References for CVE-2021-36978

cvelogic Threat Intelligence