CVE-2021-26528Public exploitNetwork attack vector

Server crash or configuration corruption via unchecked calloc

Published Feb 8, 2021 · Updated Aug 3, 2024

An out-of-bounds write in Cesanta Mongoose HTTP server 7.0 allows remote attackers to crash or corrupt a server through file requests. After repeated HTTP requests exhaust memory, mg_http_serve_file writes file and callback fields through an unchecked NULL calloc return. No authentication or user interaction is required; memory protection determines whether the result is a crash or a near-zero write to device configuration.

CVSS severity9.1
Critical
EPSS probability1.46%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

An out-of-bounds write in Cesanta Mongoose HTTP server 7.0 allows remote attackers to crash or corrupt a server through file requests. After repeated HTTP requests exhaust memory, mg_http_serve_file writes file and callback fields through an unchecked NULL calloc return. No authentication or user interaction is required; memory protection determines whether the result is a crash or a near-zero write to device configuration.

The record

CVE
CVE-2021-26528
Published
Feb 8, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 8, 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

6.4NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:P
9.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/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-787Out-of-bounds Write
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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