CVE-2023-27537Network attack vector

Application crash via unsynchronized shared HSTS state

Published Mar 30, 2023 · Updated Aug 2, 2024

Double free in libcurl 7.88.0 through 7.88.1 allows attackers to crash an application sharing HSTS state across threads. Missing mutexes or thread locks let concurrent handles sharing one HSTS cache free or access the same memory after release. Exploitation requires application-controlled cross-thread HSTS sharing and precise timing; impacts beyond a process crash are difficult.

CVSS severity5.9
Medium
EPSS probability1.86%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Double free in libcurl 7.88.0 through 7.88.1 allows attackers to crash an application sharing HSTS state across threads. Missing mutexes or thread locks let concurrent handles sharing one HSTS cache free or access the same memory after release. Exploitation requires application-controlled cross-thread HSTS sharing and precise timing; impacts beyond a process crash are difficult.

The record

CVE
CVE-2023-27537
Published
Mar 30, 2023
Updated
Aug 2, 2024
Vendor
curl
Product
curl
Classifications
CWE-415, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 30, 2023CVE publishedPublication date reported by the CVE source.
  2. Aug 2, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Fixed in 8.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

curl · curlversion=Fixed in 8.0.0

Published CVSS scores

5.9NIST NVDCVSS:3.1/AV:N/AC:H/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 exploitUnconfirmed

Weakness, pattern, technique

CWE-415Double Free
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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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