CVE-2021-26843Public exploitNetwork attack vector

Daemon crash via overlapping strcpy ranges

Published Feb 7, 2021 · Updated Aug 3, 2024

Denial of service in sthttpd 2.27.1 and earlier allows remote attackers to crash the daemon via a crafted HTTP GET filename. The de_dotdot function passes overlapping source and destination ranges to strcpy while normalizing traversal segments, invoking undefined behavior when strcpy uses memcpy. No authentication or user interaction is required; a reachable HTTP service on an affected libc implementation is enough to terminate the daemon.

CVSS severity7.5
High
EPSS probability1.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in sthttpd 2.27.1 and earlier allows remote attackers to crash the daemon via a crafted HTTP GET filename. The de_dotdot function passes overlapping source and destination ranges to strcpy while normalizing traversal segments, invoking undefined behavior when strcpy uses memcpy. No authentication or user interaction is required; a reachable HTTP service on an affected libc implementation is enough to terminate the daemon.

The record

CVE
CVE-2021-26843
Published
Feb 7, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-119, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 7, 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.

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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-119Improper Restriction of Operations within the Bounds of a Memory Buffer
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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