What is CVE-2021-39521?

CVE-2021-39521 is a medium-severity vulnerability in GNU Libredwg, classified under NULL Pointer Dereference. CVSS score: 6.5/10. Published 2021-09-20.

How severe is CVE-2021-39521?

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

Is CVE-2021-39521 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

NULL pointer dereference in GNU Libredwg

CVE-2021-39521

An issue was discovered in libredwg through v0.10.1.3751. A NULL pointer dereference exists in the function bit_read_BB() located in bits.c. It allows an attacker to cause Denial of Service.

Published 2021-09-20 · 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 (57.1th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 57th percentile — 57.1% 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

GNU Libredwg

Weakness classification (CWE)

CWE-476 — NULL Pointer Dereference

Public proof-of-concept exploits

seviezhou/Kraken

References

github.com/LibreDWG/libredwg/issues/262 (Exploit, Patch, Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2021-39521?: CVE-2021-39521 is a medium-severity vulnerability in GNU Libredwg, classified under NULL Pointer Dereference. CVSS score: 6.5/10. Published 2021-09-20.
How severe is CVE-2021-39521?: Medium severity. CVSS v3 base score is 6.5 out of 10.
Is CVE-2021-39521 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.