HOMEVULNERABILITIESCVE-2021-23017
HIGHPOC

CVE-2021-23017

CWE-193Published: June 1, 2021· Updated: Jun 17, 2026

7.7
CVSS v3.1

Official 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.

NVD Source

Technical Analysis

CVE-2021-23017 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), with a CVSS base score of 7.7.

A proof-of-concept (PoC) exploit exists for CVE-2021-23017. While not yet confirmed in active campaigns, the availability of PoC code increases exploitation risk substantially.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityHigh
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityHigh
IntegrityHigh
AvailabilityLow
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L

Affected Vendors & Products

f51 product(s)
nginx
Fedora1 product(s)
fedora
netapp1 product(s)
ontap select deploy administration utility
openresty1 product(s)
openresty
Oracle9 product(s)
blockchain platformcommunications control plane monitorcommunications fraud monitorcommunications operations monitorcommunications session border controllerenterprise communications brokerenterprise session border controllerenterprise telephony fraud monitorgoldengate
Source: NVD CPE · 25 total CPE entries

Exploit & PoC Resources

POC AVAILABLEProof-of-concept code exists
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttp://mailman.nginx.org/pipermail/nginx-announce/2021/000300.html
PATCHhttps://www.oracle.com/security-alerts/cpuapr2022.html
PATCHhttps://www.oracle.com/security-alerts/cpujan2022.html
PATCHhttps://www.oracle.com/security-alerts/cpuoct2021.html
PATCHhttp://mailman.nginx.org/pipermail/nginx-announce/2021/000300.html
PATCHhttps://www.oracle.com/security-alerts/cpuapr2022.html
PATCHhttps://www.oracle.com/security-alerts/cpujan2022.html
PATCHhttps://www.oracle.com/security-alerts/cpuoct2021.html
ADVISORYhttp://packetstormsecurity.com/files/167720/Nginx-1.20.0-Denial-Of-Service.html
ADVISORYhttps://security.netapp.com/advisory/ntap-20210708-0006/
ADVISORYhttp://packetstormsecurity.com/files/167720/Nginx-1.20.0-Denial-Of-Service.html
ADVISORYhttps://security.netapp.com/advisory/ntap-20210708-0006/

All References (28)

→
http://mailman.nginx.org/pipermail/nginx-announce/2021/000300.htmlMailing List · Patch · Vendor Advisory
→
http://packetstormsecurity.com/files/167720/Nginx-1.20.0-Denial-Of-Service.htmlThird Party Advisory · VDB Entry
→
https://lists.apache.org/thread.html/r37e6b2165f7c910d8e15fd54f4697857619ad2625f56583802004009%40%3Cnotifications.apisix.apache.org%3E
→
https://lists.apache.org/thread.html/r4d4966221ca399ce948ef34884652265729d7d9ef8179c78d7f17e7f%40%3Cnotifications.apisix.apache.org%3E
→
https://lists.apache.org/thread.html/r6fc5c57b38e93e36213e9a18c8a4e5dbd5ced1c7e57f08a1735975ba%40%3Cnotifications.apisix.apache.org%3E
→
https://lists.apache.org/thread.html/rf232eecd47fdc44520192810560303073cefd684b321f85e311bad31%40%3Cnotifications.apisix.apache.org%3E
→
https://lists.apache.org/thread.html/rf318aeeb4d7a3a312734780b47de83cefb7e6995da0b2cae5c28675c%40%3Cnotifications.apisix.apache.org%3E
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/7SFVYHC7OXTEO4SMBWXDVK6E5IMEYMEE/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GNKOP2JR5L7KCIZTJRZDCUPJTUONMC5I/
→
https://security.netapp.com/advisory/ntap-20210708-0006/Third Party Advisory
→
https://support.f5.com/csp/article/K12331123%2C
→
https://www.oracle.com/security-alerts/cpuapr2022.htmlPatch · Third Party Advisory
→
https://www.oracle.com/security-alerts/cpujan2022.htmlPatch · Third Party Advisory
→
https://www.oracle.com/security-alerts/cpuoct2021.htmlPatch · Third Party Advisory
→
http://mailman.nginx.org/pipermail/nginx-announce/2021/000300.htmlMailing List · Patch · Vendor Advisory

Quick Facts

CVE IDCVE-2021-23017
CVSS Score7.7 / 10
SeverityHIGH
WeaknessCWE-193
CISA KEVNo
ExploitPOC
Affected5 vendor(s)
PublishedJun 1, 2021

Related CVEs (CWE-193)

CVE-2024-10442
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CVE-2025-54349
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CVE-2002-0083
9.8
CVE-2003-0356
9.8
CVE-2003-0252
9.8
CVE-2025-43973
9.8

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-23017 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
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