CVE-2026-9546Public exploitNetwork attack vector

Information disclosure via uncleared Referer state

Published Jul 3, 2026 · Updated Jul 3, 2026

Information disclosure in libcurl 8.18.0 through 8.20.0 allows remote attackers to receive a stale HTTP Referer header. Curl_pretransfer leaves data->state.referer unchanged when CURLOPT_REFERER is set to NULL, so the next transfer reuses the prior value. Exposure requires an application to reuse an easy handle, set a Referer value, clear it with NULL, and then contact an unintended server; the curl command-line tool is unaffected.

CVSS severity7.5
High
EPSS probability0.49%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in libcurl 8.18.0 through 8.20.0 allows remote attackers to receive a stale HTTP Referer header. Curl_pretransfer leaves data->state.referer unchanged when CURLOPT_REFERER is set to NULL, so the next transfer reuses the prior value. Exposure requires an application to reuse an easy handle, set a Referer value, clear it with NULL, and then contact an unintended server; the curl command-line tool is unaffected.

The record

CVE
CVE-2026-9546
Published
Jul 3, 2026
Updated
Jul 3, 2026
Vendor
curl
Product
curl
Classifications
CWE-200
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 3, 2026Record 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=8.18.0 <=8.18.0
  2. Affected versionversion=8.19.0 <=8.19.0
  3. Affected versionversion=8.20.0 <=8.20.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

curl · curlversion=8.18.0 <=8.18.0; version=8.19.0 <=8.19.0; version=8.20.0 <=8.20.0

Published CVSS scores

7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

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 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-200Exposure of Sensitive Information to an Unauthorized Actor

Public exploit references

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Technologies

Your stack

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Your stack

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