---
title: "CVE-2021-23017: Off-by-one Error | CubePath"
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…"
language: en
source: https://cubepath.com/security/cve/CVE-2021-23017
---

# CVE-2021-23017: Off-by-one Error | CubePath

## 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.

Official description from the CVE record, published by f5. Copyright © 1999-2026 The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CVE license. [View the record on cve.org](https://www.cve.org/CVERecord?id=CVE-2021-23017)

## Key data

### EPSS

Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days.

Score

0.53461 (53.5% probability)

Percentile

99.0%

Scores of

Nov 10, 2026

Model

v2026.06.15

### Weakness (CWE)

CWE catalog version 5.0.

CWE names: Copyright © 2006-2026, The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CWE license.

- [CWE-193](https://cwe.mitre.org/data/definitions/193.html) Off-by-one Error

## Affected products

Products listed in the CVE record, as the CNA published them.

- Nginx Web Server, Nginx Plus

  - affected: 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

## References

Links listed in the CVE record. They lead to other sites, which CubePath does not control.

- [support.f5.com/csp/article/K12331123%2C](https://support.f5.com/csp/article/K12331123%2C)
- [mailman.nginx.org/pipermail/nginx-announce/2021/000300.html](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](https://lists.apache.org/thread.html/r6fc5c57b38e93e36213e9a18c8a4e5dbd5ced1c7e57f08a1735975ba%40%3Cnotifications.apisix.apache.org%3E)  (lists.apache.org) 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"](https://lists.apache.org/thread.html/r37e6b2165f7c910d8e15fd54f4697857619ad2625f56583802004009%40%3Cnotifications.apisix.apache.org%3E)  (lists.apache.org) 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"](https://lists.apache.org/thread.html/rf318aeeb4d7a3a312734780b47de83cefb7e6995da0b2cae5c28675c%40%3Cnotifications.apisix.apache.org%3E)  (lists.apache.org) mailing-list
- [\[apisix-notifications\] 20210608 \[GitHub\] \[apisix-website\] liuxiran merged pull request #362: docs: added "Apache APISIX not affected by NGINX CVE-2021-23017"](https://lists.apache.org/thread.html/r4d4966221ca399ce948ef34884652265729d7d9ef8179c78d7f17e7f%40%3Cnotifications.apisix.apache.org%3E)  (lists.apache.org) mailing-list
- [\[apisix-notifications\] 20210608 \[apisix-website\] branch master updated: docs: added "Apache APISIX not affected by NGINX CVE-2021-23017" (#362)](https://lists.apache.org/thread.html/rf232eecd47fdc44520192810560303073cefd684b321f85e311bad31%40%3Cnotifications.apisix.apache.org%3E)  (lists.apache.org) mailing-list
- [FEDORA-2021-b37cffac0d](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GNKOP2JR5L7KCIZTJRZDCUPJTUONMC5I/)  (lists.fedoraproject.org) vendor-advisory
- [FEDORA-2021-393d698493](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/7SFVYHC7OXTEO4SMBWXDVK6E5IMEYMEE/)  (lists.fedoraproject.org) vendor-advisory
- [oracle.com/security-alerts/cpuoct2021.html](https://www.oracle.com/security-alerts/cpuoct2021.html)
- [security.netapp.com/advisory/ntap-20210708-0006](https://security.netapp.com/advisory/ntap-20210708-0006/)
- [oracle.com/security-alerts/cpujan2022.html](https://www.oracle.com/security-alerts/cpujan2022.html)
- [oracle.com/security-alerts/cpuapr2022.html](https://www.oracle.com/security-alerts/cpuapr2022.html)
- [packetstormsecurity.com/files/167720/Nginx-1.20.0-Denial-Of…](http://packetstormsecurity.com/files/167720/Nginx-1.20.0-Denial-Of-Service.html)

## Timeline

1. ID reserved Jan 6, 2021
2. Record published Jun 1, 2021
3. Record last updated Aug 3, 2024

## Look up another CVE

## About CubePath

CubePath is a cloud provider with data centers in Europe and the United States. It offers VPS, bare metal servers and DDoS protection.

[Cloud VPS](https://cubepath.com/vps) [DDoS protection](https://cubepath.com/ddos-protection)

Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 20:03 UTC. [Sources and licenses](https://cubepath.com/security/cve/legal)