CVE-2021-33254Public exploitNetwork attack vector

Unauthenticated server crash via null host dereference

Published Jun 1, 2022 · Updated Aug 3, 2024

Null pointer dereference in EmbedThis Appweb Community Edition 8.2.1 allows remote attackers to crash the server via an invalid Host header. The parseUri function falls back to stream->host->name when the request lacks a valid Host value, but stream->host is null and the dereference causes a segmentation fault. The issue is reachable without authentication over the HTTP service and interrupts Appweb availability; confidentiality and integrity are not affected.

CVSS severity7.5
High
EPSS probability1.52%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Null pointer dereference in EmbedThis Appweb Community Edition 8.2.1 allows remote attackers to crash the server via an invalid Host header. The parseUri function falls back to stream->host->name when the request lacks a valid Host value, but stream->host is null and the dereference causes a segmentation fault. The issue is reachable without authentication over the HTTP service and interrupts Appweb availability; confidentiality and integrity are not affected.

The record

CVE
CVE-2021-33254
Published
Jun 1, 2022
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-476, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 1, 2022CVE 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

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

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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 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
T1499Endpoint Denial of Service

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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