CVE-2021-43527Public exploitNetwork attack vector

Code execution via unchecked signature length

Published Dec 8, 2021 · Updated Aug 4, 2024

Heap overflow in Mozilla Network Security Services before 3.68.1 ESR or 3.73 allows remote attackers to execute code via crafted signatures. decodeECorDSASignature in cryptohi/secvfy.c omits size checks for DSA and RSA-PSS input, then copies the decoded signature into a fixed-size VFYContext union. Exposure requires an application to verify an attacker-controlled DER signature through an affected NSS path; corruption can also crash the process or bypass signature verification.

CVSS severity9.8
Critical
EPSS probability17.56%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap overflow in Mozilla Network Security Services before 3.68.1 ESR or 3.73 allows remote attackers to execute code via crafted signatures. decodeECorDSASignature in cryptohi/secvfy.c omits size checks for DSA and RSA-PSS input, then copies the decoded signature into a fixed-size VFYContext union. Exposure requires an application to verify an attacker-controlled DER signature through an affected NSS path; corruption can also crash the process or bypass signature verification.

The record

CVE
CVE-2021-43527
Published
Dec 8, 2021
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Network Security Services (NSS)
Classifications
CWE-787
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <3.68.1
  2. Affected versionversion=unspecified <3.73

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Network Security Services (NSS)version=unspecified <3.68.1; version=unspecified <3.73

Published CVSS scores

9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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