Cloudflare: Critical Pingora Vulnerabilities Expose Cloudflare to Request Smuggling and Cache Poisoning Attacks

Cloudflare Patches Critical Pingora Flaws Enabling HTTP Request Smuggling and Cache Poisoning

In May 2025, Cloudflare disclosed multiple high-severity vulnerabilities in Pingora, its Rust-based proxy framework, which could allow attackers to smuggle HTTP requests, poison caches, and deliver malicious content at scale. The flaws, tracked under CVE-2025-4366, CVE-2026-2835, and CVE-2026-2836, exposed risks of data exposure, cross-tenant leaks, and traffic redirection particularly for organizations using Pingora with default caching settings.

Key Vulnerabilities and Exploit Paths

1. CVE-2025-4366 (HTTP/1.1 Request Smuggling & Cache Poisoning)

   • Root Cause: Pingora failed to fully drain HTTP/1.1 request bodies before reusing connections, allowing attacker-controlled bytes to be misparsed as a separate request.
   • Impact: Attackers could forge Host headers or paths, tricking downstream servers into caching malicious responses. Legitimate users would then receive attacker-controlled content, including phishing pages or malware payloads.

2. CVE-2026-2835 (HTTP/1.0 Desync & Session Hijacking)

   • Root Cause: Improper handling of HTTP/1.0 bodies and multiple Transfer-Encoding headers caused request framing desynchronization between Pingora and backend servers.
   • Impact: Attackers could bypass IP-based access controls, hijack sessions, and poison caches by pairing smuggled requests with victim traffic.

3. CVE-2026-2836 (Cross-Tenant Cache Poisoning via Weak Cache Keys)

   • Root Cause: Pingora’s default cache key relied only on URI paths, ignoring the Host/authority component.
   • Impact: In multi-tenant environments, responses from one origin could be cached and served to unrelated sites, enabling cross-tenant data leaks and widespread cache poisoning.

Cloudflare’s Response and Mitigations

Cloudflare disabled affected Pingora components in April 2025, deployed fixes, and invalidated cached assets to prevent exploitation. Key mitigations include:

• Pingora 0.5.0+: Mandates draining HTTP/1.1 request bodies before connection reuse (fixing CVE-2025-4366).
• Pingora 0.8.0+: Hardens HTTP message parsing per RFC 9112, rejecting ambiguous Transfer-Encoding sequences (resolving CVE-2026-2835).
• Cache Key Overrides: Operators must include Host/authority in cache keys to prevent cross-tenant poisoning (addressing CVE-2026-2836).

While Cloudflare’s main CDN infrastructure was partially protected by stricter ingress controls, open-source Pingora adopters remain exposed if using default caching configurations. Organizations are advised to upgrade to Pingora ≥0.8.0 and validate cache key settings in multi-tenant deployments.

Source: https://cyberpress.org/pingora-vulnerabilities/

Cloudflare cybersecurity rating report: https://www.rankiteo.com/company/cloudflare

"id": "CLO1773147283",
"linkid": "cloudflare",
"type": "Vulnerability",
"date": "5/2025",
"severity": "85",
"impact": "4",
"explanation": "Attack with significant impact with customers data leaks"

{'affected_entities': [{'customers_affected': 'Organizations using Pingora '
                                              'with default caching settings',
                        'industry': 'Cybersecurity/Cloud Services',
                        'location': 'Global',
                        'name': 'Cloudflare',
                        'size': 'Large',
                        'type': 'Technology Company'}],
 'attack_vector': 'Exploitation of improper HTTP request handling and cache '
                  'key generation in Pingora proxy framework',
 'data_breach': {'sensitivity_of_data': 'Low to Medium (depending on cached '
                                        'content)',
                 'type_of_data_compromised': ['Malicious content',
                                              'Potential cross-tenant data']},
 'date_detected': '2025-04',
 'date_publicly_disclosed': '2025-05',
 'date_resolved': '2025-05',
 'description': 'In May 2025, Cloudflare disclosed multiple high-severity '
                'vulnerabilities in Pingora, its Rust-based proxy framework, '
                'which could allow attackers to smuggle HTTP requests, poison '
                'caches, and deliver malicious content at scale. The flaws '
                'exposed risks of data exposure, cross-tenant leaks, and '
                'traffic redirection for organizations using Pingora with '
                'default caching settings.',
 'impact': {'brand_reputation_impact': 'Potential reputational damage due to '
                                       'cache poisoning and malicious content '
                                       'delivery',
            'data_compromised': ['Malicious content delivery',
                                 'Phishing pages',
                                 'Malware payloads'],
            'operational_impact': ['Traffic redirection',
                                   'Cross-tenant data leaks'],
            'systems_affected': ['Pingora proxy framework (versions before '
                                 '0.8.0)']},
 'investigation_status': 'Resolved',
 'lessons_learned': 'Importance of proper HTTP request handling, cache key '
                    'generation, and multi-tenant isolation in proxy '
                    'frameworks. Need for timely patching and validation of '
                    'default configurations.',
 'post_incident_analysis': {'corrective_actions': ['Pingora version upgrades',
                                                   'Cache key configuration '
                                                   'validation',
                                                   'HTTP message parsing '
                                                   'hardening'],
                            'root_causes': ['Improper HTTP/1.1 request body '
                                            'draining',
                                            'Ambiguous Transfer-Encoding '
                                            'header handling',
                                            'Weak cache key generation '
                                            '(URI-only)']},
 'recommendations': ['Upgrade to Pingora ≥0.8.0',
                     'Include Host/authority in cache keys for multi-tenant '
                     'deployments',
                     'Validate caching configurations'],
 'references': [{'source': 'Cloudflare Security Advisory'}],
 'response': {'containment_measures': ['Disabled affected Pingora components',
                                       'Invalidated cached assets'],
              'incident_response_plan_activated': True,
              'recovery_measures': ['Upgraded Pingora versions',
                                    'Validated cache key settings'],
              'remediation_measures': ['Released Pingora 0.5.0+ and 0.8.0+ '
                                       'with fixes',
                                       'Mandated draining HTTP/1.1 request '
                                       'bodies',
                                       'Hardened HTTP message parsing per RFC '
                                       '9112']},
 'stakeholder_advisories': 'Organizations using Pingora advised to upgrade and '
                           'validate cache key settings.',
 'title': 'Cloudflare Patches Critical Pingora Flaws Enabling HTTP Request '
          'Smuggling and Cache Poisoning',
 'type': ['HTTP Request Smuggling', 'Cache Poisoning'],
 'vulnerability_exploited': ['CVE-2025-4366', 'CVE-2026-2835', 'CVE-2026-2836']}