CVE-2021-23017: A security issue in nginx resolver was identified, which might allow an attacker who is able to forge UDP packets from the DNS server to cau
Noroxi assessment
Priority: Plan (action score 46/100)
- Public proof-of-concept code exists (Exploit-DB, GitHub); there is no record of exploitation in the wild.
- Probability of exploitation in the next 30 days: 53.4% (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. Special conditions such as timing or configuration are required.
- Fixed version: nginx (AlmaLinux:8) 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma, 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma, 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma; nginx-all-modules (AlmaLinux:8) 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma, 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma, 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma; nginx-filesystem (AlmaLinux:8) 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma, 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma, 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma.
- Mentioned 5 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).
Add it to your regular patch cycle. Upgrade to nginx (AlmaLinux:8) 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma, 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma, 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma; nginx-all-modules (AlmaLinux:8) 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma, 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma, 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma; nginx-filesystem (AlmaLinux:8) 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma, 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma, 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma 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
A security issue in nginx resolver was identified, which might allow an attacker who is able to forge UDP packets from the DNS server to cause 1-byte memory overwrite, resulting in worker process crash or potential other impact.
- BDU:2021-02749
- ALSA-2021:2259
- ALSA-2021:2290
- ALSA-2022:0323
- DLA-2670-1
- DSA-4921-1
- openSUSE-SU-2021:0835-1
- openSUSE-SU-2021:1815-1
- openSUSE-SU-2024:11092-1
- RHBA-2021:2955
- RHSA-2021:2258
- RHSA-2021:2259
- RHSA-2021:2278
- RHSA-2021:2290
- RHSA-2022:0323
- RLSA-2021:2259
- RLSA-2021:2290
- RLSA-2022:0323
- SUSE-SU-2021:1792-1
- SUSE-SU-2021:1814-1
- Published
- Jun 1, 2021
- Updated
- Jun 16, 2026
- EPSS
- 53.4% · 98th percentile
- CWE
- CWE-193
Report tools
Action score
46
Plan
Add it to your regular patch cycle.
- CVSS
- 30 / 40 · 7.7 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 16 / 30 · 53.4%
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 |
|---|---|---|
| f5 | nginx | cpe:2.3:a:f5:nginx |
| openresty | openresty | cpe:2.3:a:openresty:openresty |
| fedoraproject | fedora | cpe:2.3:o:fedoraproject:fedora |
| netapp | ontap select deploy administration utility | cpe:2.3:a:netapp:ontap_select_deploy_administration_utility |
| oracle | blockchain platform | cpe:2.3:a:oracle:blockchain_platform |
| oracle | communications control plane monitor | cpe:2.3:a:oracle:communications_control_plane_monitor |
| oracle | communications fraud monitor | cpe:2.3:a:oracle:communications_fraud_monitor |
| oracle | communications operations monitor | cpe:2.3:a:oracle:communications_operations_monitor |
| oracle | communications session border controller | cpe:2.3:a:oracle:communications_session_border_controller |
| oracle | enterprise communications broker | cpe:2.3:a:oracle:enterprise_communications_broker |
| oracle | enterprise session border controller | cpe:2.3:a:oracle:enterprise_session_border_controller |
| oracle | enterprise telephony fraud monitor | cpe:2.3:a:oracle:enterprise_telephony_fraud_monitor |
and 1 more
Using nginx? Add it to your stack and be the first to know about CVEs like this one. (Nginx)
Is nginx on your server exposed to the internet?
The free port scanner finds the open ports on your server and matches the service versions it can read against known vulnerabilities. No account needed.
Run a port scanAffected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- f5 nginx0.6.18 and later · before 1.20.1
Versions reported by the vendor
Affected version ranges reported by the assigning authority (f5). Independent of NVD's CPE analysis and usually ahead of it.
n/a Nginx Web Server, Nginx Plus
- Nginx Web Server versions 0.6.18 thru 1.20.0 before 1.20.1, Nginx plus versions R13 thru R23 before R23 P1. Nginx plus version R24 before R24 P1affected
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| AlmaLinux:8 | nginx | before 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma | 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma |
| AlmaLinux:8 | nginx | before 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma | 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma |
| AlmaLinux:8 | nginx | before 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma | 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma |
| AlmaLinux:8 | nginx | before 1:1.16.1-2.module_el8.4.0+2470+68135136.1.alma | 1:1.16.1-2.module_el8.4.0+2470+68135136.1.alma |
| AlmaLinux:8 | nginx | before 1:1.16.1-2.module_el8.5.0+35+6a1225c3.1.alma | 1:1.16.1-2.module_el8.5.0+35+6a1225c3.1.alma |
| AlmaLinux:8 | nginx | before 1:1.18.0-3.module_el8.5.0+36+48437aab.1.alma | 1:1.18.0-3.module_el8.5.0+36+48437aab.1.alma |
| AlmaLinux:8 | nginx-all-modules | before 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma | 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma |
| AlmaLinux:8 | nginx-all-modules | before 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma | 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma |
| AlmaLinux:8 | nginx-all-modules | before 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma | 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma |
| AlmaLinux:8 | nginx-all-modules | before 1:1.16.1-2.module_el8.4.0+2470+68135136.1.alma | 1:1.16.1-2.module_el8.4.0+2470+68135136.1.alma |
| AlmaLinux:8 | nginx-filesystem | before 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma | 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma |
| AlmaLinux:8 | nginx-filesystem | before 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma | 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma |
| AlmaLinux:8 | nginx-filesystem | before 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma | 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma |
| AlmaLinux:8 | nginx-filesystem | before 1:1.16.1-2.module_el8.4.0+2470+68135136.1.alma | 1:1.16.1-2.module_el8.4.0+2470+68135136.1.alma |
| AlmaLinux:8 | nginx-mod-http-image-filter | before 1:1.18.0-3.module_el8.5.0+36+48437aab.1.alma | 1:1.18.0-3.module_el8.5.0+36+48437aab.1.alma |
| AlmaLinux:8 | nginx-mod-http-image-filter | before 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma | 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma |
| AlmaLinux:8 | nginx-mod-http-image-filter | before 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma | 1:1.20.1-1.module_el8.6.0+2782+a022aca3.alma |
| AlmaLinux:8 | nginx-mod-http-image-filter | before 1:1.16.1-2.module_el8.5.0+35+6a1225c3.1.alma | 1:1.16.1-2.module_el8.5.0+35+6a1225c3.1.alma |
| AlmaLinux:8 | nginx-mod-http-image-filter | before 1:1.16.1-2.module_el8.4.0+2470+68135136.1.alma | 1:1.16.1-2.module_el8.4.0+2470+68135136.1.alma |
| AlmaLinux:8 | nginx-mod-http-image-filter | before 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma | 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma |
| AlmaLinux:8 | nginx-mod-http-perl | before 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma | 1:1.20.1-1.module_el8.5.0+2611+ab304644.alma |
| AlmaLinux:8 | nginx-mod-http-perl | before 1:1.16.1-2.module_el8.4.0+2470+68135136.1.alma | 1:1.16.1-2.module_el8.4.0+2470+68135136.1.alma |
| AlmaLinux:8 | nginx-mod-http-perl | before 1:1.18.0-3.module_el8.5.0+36+48437aab.1.alma | 1:1.18.0-3.module_el8.5.0+36+48437aab.1.alma |
| AlmaLinux:8 | nginx-mod-http-perl | before 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma | 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma |
+96
Same product
f5: all recordsOther highest-scoring records for the same primary product.
- CVE-2013-2028The ngx_http_parse_chunked function in http/ngx_http_parse.c in nginx 1.3.9 through 1.4.0 allows remote attackers to cause a denial of servi56Plan
- CVE-2016-0742The resolver in nginx before 1.8.1 and 1.9.x before 1.9.10 allows remote attackers to cause a denial of service (invalid pointer dereference55Plan
- CVE-2009-2629Buffer underflow in src/http/ngx_http_parse.c in nginx 0.1.0 through 0.5.37, 0.6.x before 0.6.39, 0.7.x before 0.7.62, and 0.8.x before 0.8.53Plan
Published before and after this one in the same product
- ← EarlierCVE-2011-4968Nov 19, 2019 · nginx http proxy module does not verify peer identity of https origin server which could facilitate man-in-the-middle attack (MITM)20Monitor
- ← EarlierCVE-2019-20372Jan 9, 2020 · NGINX before 1.17.7, with certain error_page configurations, allows HTTP request smuggling, as demonstrated by the ability of an attacker to25Monitor
- Later →CVE-2017-20005Jun 6, 2021 · NGINX before 1.13.6 has a buffer overflow for years that exceed four digits, as demonstrated by a file with a modification date in 1969 that40Plan
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 |
|---|---|---|
| almalinux:nginx | 1:1.18.0-3.module_el8.5.0+36+48437aab.1.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:nginx-all-modules | 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:nginx-filesystem | 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:nginx-mod-http-image-filter | 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:nginx-mod-http-perl | 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:nginx-mod-http-xslt-filter | 1:1.18.0-3.module_el8.5.0+36+48437aab.1.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:nginx-mod-mail | 1:1.18.0-3.module_el8.5.0+36+48437aab.1.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:nginx-mod-stream | 1:1.18.0-3.module_el8.4.0+2472+f736ed63.1.alma · AlmaLinux:8 | Package registry (OSV) |
| alpine:nginx | 1.16.1-r3 · Alpine:v3.10 | Package registry (OSV) |
| debian:nginx | 1.18.0-6.1 · Debian:12 | Package registry (OSV) |
| opensuse:nginx | 1.16.1-lp152.2.3.1 · openSUSE:Leap 15.2 | Package registry (OSV) |
| red hat:automation-hub | 0:4.2.5-1.el7pc · Red Hat:ansible_automation_platform:4.2::el7 | Package registry (OSV) |
| red hat:python-galaxy-ng | 0:4.2.5-2.el7pc · Red Hat:ansible_automation_platform:4.2::el7 | Package registry (OSV) |
| red hat:python-pulpcore | 0:3.7.6-1.el7pc · Red Hat:ansible_automation_platform:4.2::el7 | Package registry (OSV) |
| red hat:python3-galaxy-ng | 0:4.2.5-2.el7pc · Red Hat:ansible_automation_platform:4.2::el7 | Package registry (OSV) |
| red hat:python3-pulpcore | 0:3.7.6-1.el7pc · Red Hat:ansible_automation_platform:4.2::el7 | Package registry (OSV) |
| red hat:rh-nginx118-nginx | 1:1.18.0-3.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-nginx118-nginx-debuginfo | 1:1.18.0-3.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-nginx118-nginx-mod-http-image-filter | 1:1.18.0-3.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-nginx118-nginx-mod-http-perl | 1:1.18.0-3.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-nginx118-nginx-mod-http-xslt-filter | 1:1.18.0-3.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-nginx118-nginx-mod-mail | 1:1.18.0-3.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| red hat:rh-nginx118-nginx-mod-stream | 1:1.18.0-3.el7 · Red Hat:rhel_software_collections:3::el7 | Package registry (OSV) |
| rocky linux:nginx | 1:1.18.0-3.module+el8.4.0+544+e40554cf.1 · Rocky Linux:8 | Package registry (OSV) |
| suse:nginx | 1.16.1-3.15.1 · SUSE:Linux Enterprise High Performance Computing 15-ESPOS | 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
- Exploit-DB entry ×1
- Proof-of-concept repository on GitHub ×9
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 |
|---|---|---|
| Exploit-DB entry | remote | 2022-07-11 |
| Proof-of-concept repository on GitHub | stars:1 | 2021-12-17 |
| Proof-of-concept repository on GitHub | stars:136 | 2022-06-30 |
| Proof-of-concept repository on GitHub | stars:1 | 2023-07-20 |
| Proof-of-concept repository on GitHub | stars:0 | 2023-10-21 |
| Proof-of-concept repository on GitHub | stars:1 | 2024-12-08 |
| Proof-of-concept repository on GitHub | stars:0 | 2025-01-30 |
| Proof-of-concept repository on GitHub | stars:0 | 2025-04-17 |
| Proof-of-concept repository on GitHub | stars:0 | 2025-05-06 |
| Proof-of-concept repository on GitHub | stars:1 | 2025-09-04 |
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+199 d
- TodayNov 4, 2026+1982 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.
No credits in the CNA record.
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
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
National notice (Türkiye Cybersecurity Directorate / USOM)
Official security notices citing this record; remediation advice is on the agency's page.
- TR-22-0101 · Feb 1, 2022(RedHat Güvenlik Güncellemesi)
- TR-21-0685 · Aug 31, 2021(IBM Güvenlik Zafiyeti)
- TR-21-0465 · Jun 10, 2021(RedHat Güvenlik Güncellemesi Yayınladı)
- TR-21-0454 · Jun 8, 2021(RedHat Güvenlik Güncellemesi Yayınladı)
- TR-21-0438 · Jun 2, 2021(NGINX Güvenlik Zafiyeti)
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.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- high · data can be read
- Integrity
- high · data or configuration can be modified
- Availability
- low · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- Low
Weakness class (CWE)
CWE-193 · Off-by-one ErrorCVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L
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✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (13 more)Show less
- packetstormsecurity.com/files/167720/Nginx-1.20.0-Denial-Of-Service.html
- lists.apache.org/thread.html/r37e6b2165f7c910d8e15fd54f4697857619ad2625f56583802004009%40%3Cnotifications.apisix.apache.org%3E
- lists.apache.org/thread.html/r4d4966221ca399ce948ef34884652265729d7d9ef8179c78d7f17e7f%40%3Cnotifications.apisix.apache.org%3E
- lists.apache.org/thread.html/r6fc5c57b38e93e36213e9a18c8a4e5dbd5ced1c7e57f08a1735975ba%40%3Cnotifications.apisix.apache.org%3E
- lists.apache.org/thread.html/rf232eecd47fdc44520192810560303073cefd684b321f85e311bad31%40%3Cnotifications.apisix.apache.org%3E
- lists.apache.org/thread.html/rf318aeeb4d7a3a312734780b47de83cefb7e6995da0b2cae5c28675c%40%3Cnotifications.apisix.apache.org%3E
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/7SFVYHC7OXTEO4SMBWXDVK6E5IMEYMEE/
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GNKOP2JR5L7KCIZTJRZDCUPJTUONMC5I/
- security.netapp.com/advisory/ntap-20210708-0006/
- support.f5.com/csp/article/K12331123%2C
- www.oracle.com/security-alerts/cpuapr2022.html
- www.oracle.com/security-alerts/cpujan2022.html
- www.oracle.com/security-alerts/cpuoct2021.html
Vendor advisories and official records. Exploit/PoC links are deliberately left out.