How severe is CVE-2021-43527?

CVE-2021-43527 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-43527 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 18% (97th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-43527?

CVE-2021-43527 primarily affects Mozilla Nss. In total, 11 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-43527?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-43527 published?

CVE-2021-43527 was published on 2021-12-08 and last updated on 2026-06-17.

CVE-2021-43527

CVE-2021-43527 is a critical-severity vulnerability in Mozilla Nss with a CVSS 3.x base score of 9.8. Its EPSS exploit-prediction score of 18% places it in the 97th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-787.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 18% (97th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-787
Affected product: Mozilla Nss
Published: 2021-12-08
Last modified: 2026-06-17

Description

NSS (Network Security Services) versions prior to 3.73 or 3.68.1 ESR are vulnerable to a heap overflow when handling DER-encoded DSA or RSA-PSS signatures. Applications using NSS for handling signatures encoded within CMS, S/MIME, PKCS \#7, or PKCS \#12 are likely to be impacted. Applications using NSS for certificate validation or other TLS, X.509, OCSP or CRL functionality may be impacted, depending on how they configure NSS. *Note: This vulnerability does NOT impact Mozilla Firefox.* However, email clients and PDF viewers that use NSS for signature verification, such as Thunderbird, LibreOffice, Evolution and Evince are believed to be impacted. This vulnerability affects NSS < 3.73 and NSS < 3.68.1.

Frequently asked questions

What is CVE-2021-43527?: NSS (Network Security Services) versions prior to 3.73 or 3.68.1 ESR are vulnerable to a heap overflow when handling DER-encoded DSA or RSA-PSS signatures. Applications using NSS for handling signatures encoded within CMS, S/MIME, PKCS \#7, or PKCS \#12 are likely to be impacted. Applications using NSS for certificate validation or other TLS, X.509, OCSP or CRL functionality may be impacted, depending on how they configure NSS. *Note: This vulnerability does NOT impact Mozilla Firefox.* However, email clients and PDF viewers that use NSS for signature verification, such as Thunderbird, LibreOffice, Evolution and Evince are believed to be impacted. This vulnerability affects NSS < 3.73 and NSS < 3.68.1.
How severe is CVE-2021-43527?: CVE-2021-43527 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-43527 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 18% (97th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-43527?: CVE-2021-43527 primarily affects Mozilla Nss. In total, 11 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-43527?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-43527 published?: CVE-2021-43527 was published on 2021-12-08 and last updated on 2026-06-17.

References

Affected products (11)

cpe:2.3:a:mozilla:nss:*:*:*:*:*:*:*:*
cpe:2.3:a:mozilla:nss_esr:*:*:*:*:*:*:*:*
cpe:2.3:a:netapp:cloud_backup:-:*:*:*:*:*:*:*
cpe:2.3:a:netapp:e-series_santricity_os_controller:*:*:*:*:*:*:*:*
cpe:2.3:a:oracle:communications_cloud_native_core_binding_support_function:1.11.0:*:*:*:*:*:*:*
cpe:2.3:a:oracle:communications_cloud_native_core_network_repository_function:1.15.0:*:*:*:*:*:*:*
cpe:2.3:a:oracle:communications_cloud_native_core_network_repository_function:1.15.1:*:*:*:*:*:*:*
cpe:2.3:a:oracle:communications_cloud_native_core_network_slice_selection_function:1.8.0:*:*:*:*:*:*:*
cpe:2.3:a:oracle:communications_policy_management:12.6.0.0.0:*:*:*:*:*:*:*
cpe:2.3:a:starwindsoftware:starwind_san_\&_nas:v8r13:*:*:*:*:*:*:*
cpe:2.3:a:starwindsoftware:starwind_virtual_san:v8r13:14398:*:*:*:*:*:*

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