Invalid handling of X509_verify_cert() internal errors in libssl (CVE-2021-4044)
Published Sources: CVE.org, OSV
What is affected, what to do
Internally libssl in OpenSSL calls X509_verify_cert() on the client side to verify a certificate supplied by a server. That function may return a negative return value to indicate an internal error (for example out of memory).
Update node.js to version 17.3.0, openssl to version 1.0.2.
- Affected
- OpenSSL
eq Fixed in OpenSSL 3.0.1 (Affected 3.0.0)..Fixed in OpenSSL 3.0.1 (Affected 3.0.0)
- OpenSSL
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Metrics
7.5
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
7.5
CVSS v3
Severity High on the scale from 0 to 10.
Source: CVE.org, OSV
50.1 %
EPSS score
High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
Source: FIRST EPSS, percentile 98.9
Show all metrics
- Severity
- High
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 115.94 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- no public PoC known
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 7.5 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 7.5
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 50.1 %
- High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 98.9
- Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- —
- Published
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
Internally libssl in OpenSSL calls X509_verify_cert() on the client side to verify a certificate supplied by a server. That function may return a negative return value to indicate an internal error (for example out of memory). Such a negative return value is mishandled by OpenSSL and will cause an IO function (such as SSL_connect() or SSL_do_handshake()) to not indicate success and a subsequent call to SSL_get_error() to return the value SSL_ERROR_WANT_RETRY_VERIFY. This return value is only supposed to be returned by OpenSSL if the application has previously called SSL_CTX_set_cert_verify_callback(). Since most applications do not do this the SSL_ERROR_WANT_RETRY_VERIFY return value from SSL_get_error() will be totally unexpected and applications may not behave correctly as a result. The exact behaviour will depend on the application but it could result in crashes, infinite loops or other similar incorrect responses. This issue is made more serious in combination with a separate bug in OpenSSL 3.0 that will cause X509_verify_cert() to indicate an internal error when processing a certificate chain. This will occur where a certificate does not include the Subject Alternative Name extension but where a Certificate Authority has enforced name constraints. This issue can occur even with valid chains. By combining the two issues an attacker could induce incorrect, application dependent behaviour. Fixed in OpenSSL 3.0.1 (Affected 3.0.0).
Source: NVD (NIST), OSV (Open Source Vulnerabilities), cvelistv5
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| OpenSSL | OpenSSL |
|
|
| netapp | cloud_backup |
|
|
| netapp | e-series_performance_analyzer |
|
|
| netapp | ontap_select_deploy_administration_utility |
|
|
| netapp | snapcenter |
|
|
| nodejs | node.js |
|
|
| openssl | openssl |
|
|
| crates.io | openssl-src |
|
|
Vendors and products
Affected operating systems
| Other | netapp | 500f_firmware | — |
| Other | netapp | a250_firmware | — |
| Other | netapp | h300e_firmware | — |
| Other | netapp | h300s_firmware | — |
| Other | netapp | h410c_firmware | — |
| Other | netapp | h410s_firmware | — |
| Other | netapp | h500e_firmware | — |
| Other | netapp | h500s_firmware | — |
| Other | netapp | h700e_firmware | — |
| Other | netapp | h700s_firmware | — |
References & sources
- crates.iocrates/openssl-srcpackage
- rustsec.orgadvisories/RUSTSEC-2021-0129.htmladvisory
- openssl.orgnews/secadv/20211214.txtweb, x_refsource_CONFIRM, Vendor advisory
- git.openssl.orggitweb/?p=openssl.git;a=commitdiff;h=758754966791c537ea95241438…x_refsource_CONFIRM
- security.netapp.comadvisory/ntap-20211229-0003x_refsource_CONFIRM, Vendor advisory
- NVD (NIST)vuln/detail/CVE-2021-4044web
- git.openssl.orggitweb/?p=openssl.git;a=commitdiff;h=758754966791c537ea95241438…web
- security.netapp.comadvisory/ntap-20211229-0003web
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<a href="https://intel.neosec.eu/en/cve/CVE-2021-4044"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-4044.svg?lang=en" alt="CVE-2021-4044 – NEOSEC Intel" height="20"></a>