How severe is CVE-2021-36978?

CVE-2021-36978 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-36978 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (66th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-36978?

CVE-2021-36978 affects Qpdf Project Qpdf. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-36978?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-36978 published?

CVE-2021-36978 was published on 2021-07-20 and last updated on 2026-06-17.

CVE-2021-36978

CVE-2021-36978 is a medium-severity vulnerability in Qpdf Project Qpdf with a CVSS 3.x base score of 5.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-787.

Key facts

Severity: Medium (CVSS 3.x base score 5.5)
CVSS v2: 4.3
EPSS exploit prediction: 1% (66th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-787
Affected product: Qpdf Project Qpdf
Published: 2021-07-20
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is 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.
How severe is CVE-2021-36978?: CVE-2021-36978 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-36978 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (66th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-36978?: CVE-2021-36978 affects Qpdf Project Qpdf. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-36978?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-36978 published?: CVE-2021-36978 was published on 2021-07-20 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:qpdf_project:qpdf:*:*:*:*:*:*:*:*

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