CVE-2021-43527 [Critical] | Out-of-bounds Write in Nss

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.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-05-06	5.38%	5.24%	-0.14%
2	2026-04-23	5.27%	5.38%	+0.11%
3	2026-04-21	—	5.27%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-05-06

5.38%

5.24%

-0.14%

2026-04-23

5.27%

5.38%

+0.11%

2026-04-21

—

5.27%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
9.8	3.1	CRITICAL	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. 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:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	5.9	[email protected]
7.5	2.0	HIGH	`AV:N/AC:L/Au:N/C:P/I:P/A:P` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:N) No authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:P) Partial availability impact.	10.0	6.4	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

9.8

3.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
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:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

3.9

5.9

[email protected]

7.5

2.0

HIGH

AV:N/AC:L/Au:N/C:P/I:P/A:P Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:P): Partial confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:P): Partial availability impact.

10.0

6.4

[email protected]

OS Trackers for CVE-2021-43527

vendor	priority	summary	link
`alpine`	critical	CVE-2021-43527: 1 source package rows (nss); 52 state rows across 9 repos (3.12-main, 3.17-community, 3.18-community, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-community, edge-main); fixed 10, open 42.	https://security.alpinelinux.org/vuln/CVE-2021-43527
`debian`	not yet assigned	CVE-2021-43527 not yet assigned priority: Debian including 1 source packages (nss), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2021-43527
`gentoo`	high	CVE-2021-43527: 1 GLSA(s) (202212-05), 1 atom(s) (dev-libs/nss); latest impact high.	https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-43527
`redhat`	critical	—	https://access.redhat.com/security/cve/CVE-2021-43527
`suse`	high	CVE-2021-43527 severity important: SUSE including 712 source package names (1.1.1.0.1.5.568:libfreebl3-3.68.1-3.61.1, 1.1.1.0.1.5.568:libsoftokn3-3.68.1-3.61.1, …), 1898 product×package rows across 292 product lines (Container bci/bci-sle15-kernel-module-devel, Container bci/openjdk, … (292 product lines)): Fixed 1735, Known Affected 163.	https://www.suse.com/security/cve/CVE-2021-43527/
`ubuntu`	high	CVE-2021-43527 high priority: Ubuntu including 2 source packages (nss, thunderbird), 20 status rows across 10 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, trusty, upstream, xenial): released 18, DNE 1, ignored 1.	https://ubuntu.com/security/CVE-2021-43527

Affected software / configurations for CVE-2021-43527

Vendor	Product	Version	Raw CPE
mozilla	nss	< 3.73	cpe:2.3:a:mozilla:nss::::::::
mozilla	nss_esr	< 3.68.1	cpe:2.3:a:mozilla:nss_esr::::::::
netapp	cloud_backup	—	cpe:2.3:a:netapp:cloud_backup:-:::::::*
netapp	e-series_santricity_os_controller	>= 11.0, <= 11.70.1	cpe:2.3:a:netapp:e-series_santricity_os_controller::::::::
oracle	communications_cloud_native_core_binding_support_function	1.11.0	cpe:2.3:a:oracle:communications_cloud_native_core_binding_support_function:1.11.0:::::::*
oracle	communications_cloud_native_core_network_repository_function	1.15.0	cpe:2.3:a:oracle:communications_cloud_native_core_network_repository_function:1.15.0:::::::*
oracle	communications_cloud_native_core_network_repository_function	1.15.1	cpe:2.3:a:oracle:communications_cloud_native_core_network_repository_function:1.15.1:::::::*
oracle	communications_cloud_native_core_network_slice_selection_function	1.8.0	cpe:2.3:a:oracle:communications_cloud_native_core_network_slice_selection_function:1.8.0:::::::*
oracle	communications_policy_management	12.6.0.0.0	cpe:2.3:a:oracle:communications_policy_management:12.6.0.0.0:::::::*
starwindsoftware	starwind_san_\&_nas	v8r13	cpe:2.3:a:starwindsoftware:starwind_san_\&_nas:v8r13:::::::*
starwindsoftware	starwind_virtual_san	v8r13	cpe:2.3:a:starwindsoftware:starwind_virtual_san:v8r13:14398::::::

References for CVE-2021-43527

URL	Tags
https://bugzilla.mozilla.org/show_bug.cgi?id=1737470	Issue Tracking Permissions Required Vendor Advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-594438.pdf	Third Party Advisory
https://ftp.mozilla.org/pub/security/nss/releases/NSS_3_68_1_RTM/	Vendor Advisory
https://ftp.mozilla.org/pub/security/nss/releases/NSS_3_73_RTM/	Vendor Advisory
https://security.gentoo.org/glsa/202212-05	Third Party Advisory
https://security.netapp.com/advisory/ntap-20211229-0002/	Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-51/	Vendor Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html	Patch Third Party Advisory
https://www.starwindsoftware.com/security/sw-20220802-0001/	Third Party Advisory

URL

CVE-2021-43527

Exploit prediction scoring system (EPSS) score for CVE-2021-43527

Common vulnerability scoring system (CVSS) metrics for CVE-2021-43527

Weakness enumeration for CVE-2021-43527

OS Trackers for CVE-2021-43527

Affected software / configurations for CVE-2021-43527

References for CVE-2021-43527