CVE-2021-4044: Invalid handling of X509_verify_cert() internal errors in libssl
Noroxi assessment
Priority: Plan (action score 45/100)
- Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
- Probability of exploitation in the next 30 days: 50% (FIRST EPSS); higher than 98.9% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
- Fixed version: openssl3 (Alpine:v3.15) 3.0.2-r0; openssl3 (Alpine:v3.16) 3.0.1-r0; openssl (Alpine:v3.17) 3.0.1-r0.
Add it to your regular patch cycle. Upgrade to openssl3 (Alpine:v3.15) 3.0.2-r0; openssl3 (Alpine:v3.16) 3.0.1-r0; openssl (Alpine:v3.17) 3.0.1-r0 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
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).
- Published
- Dec 14, 2021
- Updated
- Jun 17, 2026
- EPSS
- 50.0% · 98th percentile
- CWE
- CWE-835
Report tools
Action score
45
Plan
Add it to your regular patch cycle.
- CVSS
- 30 / 40 · 7.5 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 15 / 30 · 50.0%
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- Proof of concept exists, no weaponized module
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| openssl | openssl | cpe:2.3:a:openssl:openssl |
| netapp | h500e | cpe:2.3:h:netapp:h500e |
| netapp | h700e firmware | cpe:2.3:o:netapp:h700e_firmware |
| netapp | h700e | cpe:2.3:h:netapp:h700e |
| netapp | cloud backup | cpe:2.3:a:netapp:cloud_backup |
| netapp | e-series performance analyzer | cpe:2.3:a:netapp:e-series_performance_analyzer |
| netapp | ontap select deploy administration utility | cpe:2.3:a:netapp:ontap_select_deploy_administration_utility |
| netapp | snapcenter | cpe:2.3:a:netapp:snapcenter |
| netapp | a250 firmware | cpe:2.3:o:netapp:a250_firmware |
| netapp | a250 | cpe:2.3:h:netapp:a250 |
| netapp | 500f firmware | cpe:2.3:o:netapp:500f_firmware |
| netapp | 500f | cpe:2.3:h:netapp:500f |
and 14 more
Check your server's TLS configuration
The OpenSSL version can't be seen from outside; the free SSL checker tests your certificate, enabled TLS versions and weak ciphers. Confirm the version on your server with the package manager.
Run the SSL checkAffected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- nodejs node.js17.0.0 and later · before 17.3.0
Versions reported by the vendor
Affected version ranges reported by the assigning authority (openssl). Independent of NVD's CPE analysis and usually ahead of it.
OpenSSL OpenSSL
- Fixed in OpenSSL 3.0.1 (Affected 3.0.0)affected
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Alpine:v3.15 | openssl3 | before 3.0.2-r0 | 3.0.2-r0 |
| Alpine:v3.16 | openssl3 | before 3.0.1-r0 | 3.0.1-r0 |
| Alpine:v3.17 | openssl | before 3.0.1-r0 | 3.0.1-r0 |
| crates.io | openssl-src | from 300.0.0 · before 300.0.4 | 300.0.4 |
| openSUSE:Tumbleweed | openssl-3 | before 3.0.1-1.1 | 3.0.1-1.1 |
Same product
openssl: all recordsOther highest-scoring records for the same primary product.
- CVE-2014-0160The (1) TLS and (2) DTLS implementations in OpenSSL 1.0.1 before 1.0.1g do not properly handle Heartbeat Extension packets, which allows remKEV90Now
- CVE-2021-3711SM2 Decryption Buffer Overflow65This week
- CVE-2003-0545Double free vulnerability in OpenSSL 0.9.7 allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code 65This week
Published before and after this one in the same product
- ← EarlierCVE-2021-3450Mar 25, 2021 · CA certificate check bypass with X509_V_FLAG_X509_STRICT35Monitor
- ← EarlierCVE-2021-3712Aug 24, 2021 · Read buffer overruns processing ASN.1 strings44Plan
- Later →CVE-2021-4160Jan 28, 2022 · BN_mod_exp may produce incorrect results on MIPS24Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| alpine:openssl | 3.0.1-r0 · Alpine:v3.17 | Package registry (OSV) |
| alpine:openssl3 | 3.0.2-r0 · Alpine:v3.15 | Package registry (OSV) |
| crates.io:openssl-src | 300.0.4 | Package registry (OSV) |
| opensuse:openssl-3 | 3.0.1-1.1 · openSUSE:Tumbleweed | Package registry (OSV) |
Exploit status
Proof of concept available
A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.
Evidence
- Proof-of-concept repository on GitHub ×1
Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.
| Source | Kind | Date |
|---|---|---|
| Proof-of-concept repository on GitHub | stars:0 | 2024-09-05 |
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
- Published
- First PoC+995 d
- TodayNov 2, 2026+1784 d
No history yet (it accumulates with the daily EPSS job).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- none
- Integrity
- none
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- None
- Availability impact
- High
Weakness class (CWE)
CWE-835 · Loop with Unreachable Exit Condition ('Infinite Loop')CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log
- Fix✗ → ✓
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References
Show all references (2 more)Show less
Vendor advisories and official records. Exploit/PoC links are deliberately left out.