CVE-2021-28839Public exploitNetwork attack vector

Unauthenticated HTTP crash via NULL strrchr argument

Published Aug 10, 2021 · Updated Aug 3, 2024

Null pointer dereference in D-Link DAP firmware allows remote attackers to crash the HTTP service via a crafted HTTP GET request. The sbin/httpd upload_certificate function passes a NULL first argument to strrchr while processing the request, terminating the web service. The unauthenticated network path affects the nine documented firmware builds; the reported consequence is service interruption, not data access or modification.

CVSS severity7.5
High
EPSS probability1.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Null pointer dereference in D-Link DAP firmware allows remote attackers to crash the HTTP service via a crafted HTTP GET request. The sbin/httpd upload_certificate function passes a NULL first argument to strrchr while processing the request, terminating the web service. The unauthenticated network path affects the nine documented firmware builds; the reported consequence is service interruption, not data access or modification.

The record

CVE
CVE-2021-28839
Published
Aug 10, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-476, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 10, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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