Description
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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| — | 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 P1 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | nginx | 1.18.0-6.1 | — |
| Debian 13 | nginx | 1.18.0-6.1 | — |
| Debian 12 | nginx | 1.18.0-6.1 | — |
| Debian 10 | nginx | 1.14.2-2+deb10u4 | DSA-4921-1 |
| Debian 9 | nginx | 1.10.3-1+deb9u6 | DLA-2670-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 20.04 LTS | nginx | 1.18.0-0ubuntu1.2 | USN-4967-1 |
| Ubuntu 18.04 LTS | nginx | 1.14.0-0ubuntu1.9 | USN-4967-1 |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 16.04 LTS | nginx | 1.10.3-0ubuntu0.16.04.5+esm1 | USN-4967-2 |
| Ubuntu Pro 14.04 LTS | nginx | 1.4.6-1ubuntu3.9+esm2 | USN-4967-2 |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 8 | nginx +7 | 1:1.16.1-2.module+el8.4.0+11155+68135136.1 | RHSA-2022:0323, RHSA-2021:2290, RHSA-2021:2259 |
| RHEL 3 | rh-nginx116-nginx +5 | 1:1.16.1-6.el7 | RHSA-2021:2278 |
| RHEL 3 | rh-nginx118-nginx +5 | 1:1.18.0-3.el7 | RHSA-2021:2258 |
Show 3 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 8.2 EUS | nginx +7 | 1:1.16.1-1.module+el8.2.0+11154+636e4c3b.1 | RHSA-2021:2290 |
| RHEL 8.1 EUS | nginx +7 | 1:1.16.1-1.module+el8.1.0+11153+6c3a40a9.1 | RHSA-2021:2290 |
| Red Hat Ansible Automation Platform 4 | automation-hub | 4.2.5-1.el7pc | RHBA-2021:2955 |
| Red Hat Ansible Automation Platform 4 | python-galaxy-ng +1 | 4.2.5-2.el7pc | RHBA-2021:2955 |
| Red Hat Ansible Automation Platform 4 | python-pulpcore +1 | 3.7.6-1.el7pc | RHBA-2021:2955 |
AlmaLinux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux 8 | nginx +7 | 1:1.16.1-2.module_el8.4.0+2470+68135136.1.alma | ALSA-2022:0323, ALSA-2021:2290, ALSA-2021:2259 |
Rocky Linux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Rocky Linux 8 | nginx | 1:1.16.1-2.module+el8.4.0+543+efbf198b.1 | RLSA-2022:0323, RLSA-2021:2290, RLSA-2021:2259 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP3 | nginx | 1.19.8-3.3.1 | SUSE-SU-2021:1815-1 |
| SLES 15 SP2 | nginx | 1.16.1-3.3.1 | SUSE-SU-2021:1814-1 |
| SLES 15 SP1 | nginx | 1.16.1-6.13.1 | SUSE-SU-2021:1839-1 |
| SLES 15 | nginx | 1.16.1-3.15.1 | SUSE-SU-2021:1792-1 |
Show 8 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 15 SP1 | nginx | 1.16.1-6.13.1 | SUSE-SU-2021:1839-1 |
| SLES for SAP 15 | nginx | 1.16.1-3.15.1 | SUSE-SU-2021:1792-1 |
| SLE HPC 15 SP1 | nginx | 1.16.1-6.13.1 | SUSE-SU-2021:1839-1 |
| SLE HPC 15 | nginx | 1.16.1-3.15.1 | SUSE-SU-2021:1792-1 |
| SUSE Manager Server 4.0 | nginx | 1.16.1-6.13.1 | SUSE-SU-2021:1839-1 |
| SUSE Manager Retail Branch Server 4.0 | nginx | 1.16.1-6.13.1 | SUSE-SU-2021:1839-1 |
| SUSE Manager Proxy 4.0 | nginx | 1.16.1-6.13.1 | SUSE-SU-2021:1839-1 |
| SUSE Enterprise Storage 6 | nginx | 1.16.1-6.13.1 | SUSE-SU-2021:1839-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | nginx | 1.21.3-1.4 | openSUSE-SU-2024:11092-1 |
| openSUSE Leap 15.3 | nginx | 1.19.8-3.3.1 | openSUSE-SU-2021:1815-1 |
| openSUSE Leap 15.2 | nginx | 1.16.1-lp152.2.3.1 | openSUSE-SU-2021:0835-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | nginx | 1.20.1-r0 | — |
| Alpine v3.23 | nginx | 1.20.1-r0 | — |
| Alpine v3.22 | nginx | 1.20.1-r0 | — |
| Alpine v3.21 | nginx | 1.20.1-r0 | — |
| Alpine v3.20 | nginx | 1.20.1-r0 | — |
Show 10 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.19 | nginx | 1.20.1-r0 | — |
| Alpine v3.18 | nginx | 1.20.1-r0 | — |
| Alpine v3.17 | nginx | 1.20.1-r0 | — |
| Alpine v3.16 | nginx | 1.20.1-r0 | — |
| Alpine v3.15 | nginx | 1.20.1-r0 | — |
| Alpine v3.14 | nginx | 1.20.1-r0 | — |
| Alpine v3.13 | nginx | 1.18.0-r14 | — |
| Alpine v3.12 | nginx | 1.18.0-r2 | — |
| Alpine v3.11 | nginx | 1.16.1-r7 | — |
| Alpine v3.10 | nginx | 1.16.1-r3 | — |
Oracle Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Oracle Linux 8 | nginx +7 | 1:1.16.1-2.0.1.module+el8.4.0+20188+a733e426.1 | ELSA-2022-0323, ELSA-2021-2290, ELSA-2021-2259 |
Public exploits
Exploit or proof-of-concept code for this vulnerability is publicly available, which lowers the bar for attackers. Treat it as a reason to patch sooner.
Third-party code, not reviewed by us. Public PoCs are sometimes fake or contain malware. Read the code first and run it only in an isolated lab, against systems you are authorised to test.
Exploit-DB 1
- Nginx 1.20.0 - Denial of Service (DOS) EDB-50973 · remote · Jul 11, 2022
GitHub 9 repositories
-
M507/CVE-2021-23017-PoC ★ 138 · Jun 30, 2022
PoC for Nginx 0.6.18 - 1.20.0 Memory Overwrite Vulnerability CVE-2021-23017
-
6lj/EVIL-CVE-2021-23017-Update-2025 ★ 1 · Sep 4, 2025
vulnerability in NGINX servers (versions 0.6.18–1.20.0). The scripts aim to cause a Denial of Service (DoS) by sending malicious DNS responses, with enhancements to bypass firewalls.
-
z3usx01/CVE-2021-23017-POC ★ 1 · Dec 8, 2024
The issue only affects nginx if the "resolver" directive is used in the configuration file. Further, the attack is only possible if an attacker is able to forge UDP packets from the DNS server.
-
lakshit1212/CVE-2021-23017-PoC ★ 1 · Jul 20, 2023
-
niandy/nginx-patch ★ 1 · Dec 17, 2021
nginx 1.15.10 patch against cve-2021-23017 (ingress version)
-
moften/CVE-2021-23017 ★ 0 · May 6, 2025
NGINX DNS Overflow Vulnerability Check - CVE-2021-23017 PoC
-
Cybervixy/Vulnerability-Management ★ 0 · Apr 17, 2025
NGINX Security Hardening & Vulnerability Remediation Analysis of critical CVEs (CVE-2021-23017, HTTP/2 DoS flaws) in outdated NGINX versions, with actionable steps for mitigation: upgrades, HTTP/2 ha…
-
lukwagoasuman/-home-lukewago-Downloads-CVE-2021-23017-Nginx-1.14 ★ 0 · Jan 30, 2025
-
ShivamDey/CVE-2021-23017 ★ 0 · Oct 21, 2023
Sources: PoC-in-GitHub, Metasploit Framework, Exploit-DB — updated daily. Only links are listed; no exploit code is hosted here.
Advisories 31
- ALSA-2021:2290 Important: nginx:1.16 security update AlmaLinux Security Advisories · Oct 29, 2026
- ALSA-2021:2259 Important: nginx:1.18 security update AlmaLinux Security Advisories · Oct 29, 2026
- ALSA-2022:0323 Important: nginx:1.20 security update AlmaLinux Security Advisories · Oct 29, 2026
- RHSA-2022:0323 Red Hat Security Advisory: nginx:1.20 security update Red Hat Security Advisories (RHSA) · Aug 5, 2026
- RHSA-2021:2290 Red Hat Security Advisory: nginx:1.16 security update Red Hat Security Advisories (RHSA) · Aug 5, 2026
- RHSA-2021:2259 Red Hat Security Advisory: nginx:1.18 security update Red Hat Security Advisories (RHSA) · Aug 5, 2026
- RHSA-2021:2278 Red Hat Security Advisory: rh-nginx116-nginx security update Red Hat Security Advisories (RHSA) · Aug 5, 2026
- RHSA-2021:2258 Red Hat Security Advisory: rh-nginx118-nginx security update Red Hat Security Advisories (RHSA) · Aug 5, 2026
- RHBA-2021:2955 Red Hat Bug Fix Advisory: Red Hat Automation Platform 1.2.4 Red Hat Security Advisories (RHSA) · Aug 5, 2026
- WID-SEC-2022-0463 NGINX: Schwachstelle ermöglicht Denial of Service BSI CERT-Bund (WID) · Jul 14, 2026
- USN-4967-2 nginx vulnerability Ubuntu Security Notices (USN) · Jun 29, 2026
- DSA-4921-1 nginx - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DLA-2670-1 nginx - security update Debian Security (DSA / DLA) · Mar 9, 2026
- USN-4967-1 nginx vulnerability Ubuntu Security Notices (USN) · Feb 10, 2026
- RLSA-2022:0323 Important: nginx:1.20 security update Rocky Linux Security Advisories · Feb 5, 2026
- RLSA-2021:2259 Important: nginx:1.18 security update Rocky Linux Security Advisories · Feb 4, 2026
- RLSA-2021:2290 Important: nginx:1.16 security update Rocky Linux Security Advisories · Feb 4, 2026
- openSUSE-SU-2021:0835-1 Security update for nginx SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:1814-1 Security update for nginx SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:1792-1 Security update for nginx SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:1839-1 Security update for nginx SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2021:1815-1 Security update for nginx SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2024:11092-1 nginx-1.21.3-1.4 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
- SCA-2025-0011 Vulnerabilities affecting Endress+Hauser SSG-E210GC SICK PSIRT · Oct 2, 2025
- SCA-2025-0009 Vulnerabilities affecting SICK TDC-E210GC SICK PSIRT · Aug 1, 2025
- VDE-2022-010 PHOENIX CONTACT: Multiple Linux component vulnerabilities fixed in latest AXC F x152 LTS release CERT@VDE · May 22, 2025
- SUSE-SU-2021:1815-1 Security update for nginx SUSE / openSUSE Security Updates · May 2, 2025
- WID-SEC-2022-0676 Juniper Junos Space: Mehrere Schwachstellen BSI CERT-Bund (WID) · Jan 11, 2023
- ELSA-2022-0323 Important: nginx:1.20 security update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Feb 1, 2022
- ELSA-2021-2290 Important: nginx:1.16 security update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Jun 10, 2021
- ELSA-2021-2259 Important: nginx:1.18 security update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Jun 8, 2021
References
- https://support.f5.com/csp/article/K12331123%2C
- http://mailman.nginx.org/pipermail/nginx-announce/2021/000300.html
- [apisix-notifications] 20210607 [GitHub] [apisix-website] Serendipity96 opened a new pull request #362: feat: add new blog mailing-list
- [apisix-notifications] 20210608 [GitHub] [apisix-website] liuxiran commented on a change in pull request #362: docs: added "Apache APISIX not affected by NGINX CVE-2021-23017" mailing-list
- [apisix-notifications] 20210608 [GitHub] [apisix-website] netlify[bot] edited a comment on pull request #362: docs: added "Apache APISIX not affected by NGINX CVE-2021-23017" mailing-list
- [apisix-notifications] 20210608 [GitHub] [apisix-website] liuxiran merged pull request #362: docs: added "Apache APISIX not affected by NGINX CVE-2021-23017" mailing-list
- [apisix-notifications] 20210608 [apisix-website] branch master updated: docs: added "Apache APISIX not affected by NGINX CVE-2021-23017" (#362) mailing-list
- FEDORA-2021-b37cffac0d vendor-advisory
- FEDORA-2021-393d698493 vendor-advisory
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://security.netapp.com/advisory/ntap-20210708-0006/
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://www.oracle.com/security-alerts/cpuapr2022.html
- http://packetstormsecurity.com/files/167720/Nginx-1.20.0-Denial-Of-Service.html