CVE-2021-40540Public exploitNetwork attack vector

Unauthenticated service crash via uninitialized request state

Published Sep 7, 2021 · Updated Aug 4, 2024

Memory corruption in Ulfius HTTP Framework before 2.7.4 allows remote attackers to crash services via malformed HTTP requests. ulfius_uri_logger leaves its connection-info allocation partly uninitialized, so cleanup can act on an invalid request pointer and double-free heap memory. No authentication or user interaction is required; two crafted requests can trigger a segmentation fault or abort, while code execution remains unproven.

CVSS severity9.8
Critical
EPSS probability2.63%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory corruption in Ulfius HTTP Framework before 2.7.4 allows remote attackers to crash services via malformed HTTP requests. ulfius_uri_logger leaves its connection-info allocation partly uninitialized, so cleanup can act on an invalid request pointer and double-free heap memory. No authentication or user interaction is required; two crafted requests can trigger a segmentation fault or abort, while code execution remains unproven.

The record

CVE
CVE-2021-40540
Published
Sep 7, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/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

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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