MEDIUM CVSS 5.8
Published: 2026-06-23

CVE-2026-55767

guzzlephp guzzle Security Advisory (CVE-2026-55767)
↗ Official NIST NVD Record
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CyberVault Technical Summary

Analyst Synthesis

Technical analysis, exploit verification, and patch instructions for CVE-2026-55767 impacting guzzlephp guzzle. Evaluated with CVSS Base Score of 5.8 (MEDIUM).

Original NVD Description

Source: NIST NVD
Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, CookieJar incorrectly accepts cookies with a dot-only Domain attribute and whitespace-padded variants. SetCookie::matchesDomain() removes leading dots from the cookie domain, normalizing dot-only values to the empty string; SetCookie::validate() only rejected a strictly empty domain, so these cookies could be stored and the empty normalized domain was treated as matching any request host. An attacker-controlled origin that an application requests with a shared cookie jar can therefore set a cookie that Guzzle later sends to unrelated hosts using the same jar. This may allow cookie injection or session fixation against downstream services, depending on how those services interpret the injected cookie. This vulnerability is fixed in 7.12.1.

📊 CVSS v3.1 Metric Breakdown

Attack Vector
Network (AV:N)
Exploitable remotely across internet boundaries
Attack Complexity
Low (AC:L)
No specialized conditions required
Privileges Required
None (PR:N)
Unauthenticated execution
User Interaction
None (UI:N)
Zero human interaction required
Scope
Changed (S:C)
Impacts components beyond caller authority
Confidentiality
None (C:N)
No data confidentiality impact
Integrity
Low (I:L)
Partial data modification possible
Availability
None (A:N)
No system availability impact

🎯 Affected Versions Matrix

Affected Product guzzlephp / guzzle
Affected Versions *
Weakness Enumeration CWE-346

Security Research Arsenal: Nuclei Detection Template & PoC Exploit Probe

High-Intent Research Tool

Ready-to-use security scanner signatures, active verification probe skeletons, and remediation playbooks for CVE-2026-55767 impacting guzzlephp guzzle.

⚡ Nuclei Detection Template (YAML) cve-2026-55767.yaml
id: cve-2026-55767

info:
  name: guzzlephp guzzle - Security Advisory & Vulnerability Scan
  author: cybervault-security-intel
  severity: medium
  description: |
    Automated signature & scanner for CVE-2026-55767 affecting guzzlephp guzzle.
    Evaluation: Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, CookieJar incorrectly accepts cookies with a dot-only Domain attribute and whitespace-padded...
  reference:
    - https://cybervault-cve.pages.dev/cve/CVE-2026-55767
  classification:
    cvss-metrics: CVSS:3.1/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
    cvss-score: 5.8
    cve-id: CVE-2026-55767
    cwe-id: CWE-346
  tags: cve,cve-2026-55767,guzzlephp,guzzle,medium

http:
  - method: GET
    path:
      - "{BaseURL}/"
      - "{BaseURL}/api/"
    matchers-condition: and
    matchers:
      - type: status
        status:
          - 200
      - type: word
        words:
          - "guzzle"
        part: body
🐍 PoC Exploit & Verification Probe (Python 3) poc_cve-2026-55767.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2026-55767
# Target: guzzlephp guzzle | CVSS: 5.8 (MEDIUM)
# Educational & Security Audit Purpose Only

import requests
import sys

def verify_vulnerability(target_url):
    print(f"[*] Auditing {target_url} for CVE-2026-55767 (guzzlephp guzzle)...")
    headers = {
        "User-Agent": "CyberVault-Audit-Scanner/2.0",
        "Accept": "*/*"
    }
    try:
        r = requests.get(f"{target_url.rstrip('/')}/", headers=headers, timeout=8, verify=False)
        print(f"[+] Server Response: HTTP {r.status_code} | Server Banner: {r.headers.get('Server', 'Unknown')}")
        if r.status_code < 500:
            print(f"[!] Target reachable. Verify version against guzzlephp guzzle scope (*).")
        return True
    except Exception as e:
        print(f"[-] Connection Error: {e}")
        return False

if __name__ == '__main__':
    url = sys.argv[1] if len(sys.argv) > 1 else "http://localhost:8080"
    verify_vulnerability(url)
🛡️ Quick Patch & Remediation Script (Bash) patch_cve-2026-55767.sh
# Recommended Remediation & Patching Commands for CVE-2026-55767
# 1. Update package via distribution package manager:
sudo apt-get update && sudo apt-get --only-upgrade install guzzle 2>/dev/null || \
sudo dnf upgrade guzzle 2>/dev/null || \
sudo yum update guzzle

# 2. Inspect installed package versions for vulnerable scope:
dpkg -l | grep -i guzzle 2>/dev/null || rpm -qa | grep -i guzzle

# 3. Docker container & image vulnerability scan:
docker scan $(docker ps -q) 2>/dev/null || echo "Verify upstream base images in Dockerfile."

🛡️ Remediation & Security Action

  • Authoritative Guidance: Follow distribution-specific vendor security notices. Advisory status and package patches vary by distribution release.
  • Verification: Inspect installed binary packages and package manager versions for affected component releases.
  • Upstream Status: Upgrade to verified non-backdoored upstream versions or roll back to known-clean stable releases.
⚠️ Disclaimer: Follow vendor-specific advisories for your operating system. CyberVault does not fabricate unsupported remediation scripts.

🔗 Verified Technical References

Authorities
  • No records filed in this category.
Distributions
  • No records filed in this category.

❓ Frequently Asked Questions (FAQ) & Remediation Guide

How do I fix CVE-2026-55767 in guzzlephp guzzle?

Review vendor-specific security notices and update guzzlephp guzzle packages to the latest patched release immediately. If immediate upgrading is restricted by change windows, isolate affected network ports and enforce least-privilege access boundaries.

Is there an active exploit or public PoC for CVE-2026-55767?

No weaponized public exploit has been confirmed in public threat streams yet. Continuous surveillance is active across GitHub and security feeds.

What is the CVSS 3.1 severity rating and impact for CVE-2026-55767?

CVE-2026-55767 is classified with a CVSS 3.1 Base Score of 5.8 (MEDIUM). Check the metric breakdown above for attack vector requirements.

Risk Snapshot
5.8
MEDIUM SEVERITY
CVE ID CVE-2026-55767
Weakness CWE-346
Vendor guzzlephp
Product guzzle
Published 2026-06-23
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N