CVE-2021-4044
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Invalid handling of X509_verify_cert() internal errors in libssl
rank 49 = 23 + 19 + 2 + 5 + 0
rank@v1 · this cycle
Someone is already using it
CISA KEV catalog · public proof-of-concept · FIRST EPSS
EPSS 0.50099 · without this subject the record ranks 26
What it costs you if it fires
NVD CVSS base score, then the CNA's own
CVSS 7.5, from NVD · without this subject the record ranks 30
It is getting worse, not staying still
FIRST EPSS series, rescorings and bad loads removed
rose on 2026-04-20 · without this subject the record ranks 47
How much of the world it touches
NVD CPE configurations
4 products in the CPE ranges · without this subject the record ranks 44
Someone else already set the date
CISA KEV remediation due date
no CISA due date · without this subject the record ranks 49
$1.53M = $4.99M incident cost x 0.6121449559255632 exposure x 0.50099 likelihood
udv@v1 · unaudited · wrong for you until you say what you run
$4.99M is the cost of a breach that happened, from IBM Cost of a Data Breach Report 2026, global average. It is not the value of any asset of yours. That average already covers breaches of every severity, so scaling it by exposure understates a partial-impact record. That is an assumption, not a measurement. Your own asset value goes in the decision record.
Hindsight · the state
Foresight · where to check next
No weakness class or product neighbourhood is held for this record, so this index cannot name anywhere to check next. That is an absence in the record, not a finding about the software.
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Exploit Status & Known PoCs a ladder, not a score
Current rung: Proof-of-concept published · 1 public repository, 2024-09-05.
- RUNG 1Nothing observed in held sources
- RUNG 2Proof-of-concept published · 1 public repository2024-09-05receipt
- RUNG 3Exploited in the wild · CISA KEV listed
- RUNG 4Ransomware campaign use known
A rung lights from a row in the index, never from an assessment. "Held sources" is the true scope of the claim: this index reads the CVE record, NVD, CISA KEV, FIRST's EPSS and public proof-of-concept repositories, and it does not observe attacks.
What it is stated by the CNA
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(). receipt
Read the rest of the CNA's description
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).
NVD's analysis a second authority
- severity
- 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- weakness
- CWE-835
- affected versions
- openssl < 1.0.2; openssl 1.1.0; openssl 3.0.0; and 1 more, listed in full below
check it yourself openssl.org git.openssl.org security.netapp.com receipt
Dated events
Movement the material steps
This score more than doubled inside 72 hours. Both observations are in the full history below.
Show all 66 observations
66 observations held. A highlighted step crossed a promotion threshold. A step marked with a scoring model moved because the instrument was replaced, not because the vulnerability changed. receipt
Siblings and hubs
Records related to this one
No record cites this identifier and it carries no alias. Its defect family is below.
Its defect family
openssl
Of the 2 records in this family, this is the only one with public proof-of-concept code, and it holds 1 references to it.
Grouped by shared product and weakness, not by shared vulnerability. Each record's own state is on its own page.
Family membership: held values
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What usually comes next
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