CVE-2026-55568Network attack vector

Credential disclosure via silent HTTPS-proxy downgrade

Published Jun 23, 2026 · Updated Jun 23, 2026

Cleartext transmission in Guzzle before 7.12.1 allows remote attackers to read proxy credentials and proxy negotiation metadata. CurlHandler and CurlMultiHandler pass an HTTPS proxy to libcurl without first verifying HTTPS-proxy support, allowing libcurl before 7.50.2 to treat it as plaintext HTTP without an error. Exposure requires the built-in cURL handlers, an HTTPS proxy configured with expected hop encryption, and libcurl before 7.50.2; inner TLS still protects tunneled HTTPS payloads.

CVSS severity5.9
Medium
EPSS probability0.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cleartext transmission in Guzzle before 7.12.1 allows remote attackers to read proxy credentials and proxy negotiation metadata. CurlHandler and CurlMultiHandler pass an HTTPS proxy to libcurl without first verifying HTTPS-proxy support, allowing libcurl before 7.50.2 to treat it as plaintext HTTP without an error. Exposure requires the built-in cURL handlers, an HTTPS proxy configured with expected hop encryption, and libcurl before 7.50.2; inner TLS still protects tunneled HTTPS payloads.

The record

CVE
CVE-2026-55568
Published
Jun 23, 2026
Updated
Jun 23, 2026
Vendor
Guzzle
Product
Guzzle
Classifications
CWE-319, CWE-636, CWE-311, T1040
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 23, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 23, 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=< 7.12.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Guzzle · Guzzleversion=< 7.12.1

Published CVSS scores

5.9GitHubCVSS:3.1/AV:N/AC:H/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 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-319Cleartext Transmission of Sensitive Information
CWE-636Not Failing Securely ('Failing Open')
CWE-311Missing Encryption of Sensitive Data
T1040Network Sniffing

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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