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    CVE-2016-3739

    The (1) mbed_connect_step1 function in lib/vtls/mbedtls.c and (2) polarssl_connect_step1 function in lib/vtls/polarssl.c in cURL and libcurl before 7.49.0, when using SSLv3 or making a TLS connection to a URL that uses a numerical IP address, allow remote attackers to spoof servers via an arbitrary valid certificate.

    Published:May 18, 2016
    Last Modified:Apr 12, 2025
    EPS:May 20, 2016
    EPSS Score:0.01068
    CVSS Score:5.3

    Affected Products

    Vendor
    Haxx
    Product
    Curl

    Exploits

    No exploit reference

    Common Attack Pattern Enumeration and Classification (CAPEC)

    CAPEC-10 Buffer Overflow via Environment Variables
    CAPEC-101 Server Side Include (SSI) Injection
    CAPEC-104 Cross Zone Scripting
    CAPEC-108 Command Line Execution through SQL Injection
    CAPEC-109 Object Relational Mapping Injection
    CAPEC-110 SQL Injection through SOAP Parameter Tampering
    CAPEC-111 JSON Hijacking (aka JavaScript Hijacking)
    CAPEC-120 Double Encoding
    CAPEC-13 Subverting Environment Variable Values
    CAPEC-135 Format String Injection
    CAPEC-136 LDAP Injection
    CAPEC-14 Client-side Injection-induced Buffer Overflow
    CAPEC-141 Cache Poisoning
    CAPEC-142 DNS Cache Poisoning
    CAPEC-148 Content Spoofing
    CAPEC-153 Input Data Manipulation
    CAPEC-182 Flash Injection
    CAPEC-209 XSS Using MIME Type Mismatch
    CAPEC-218 Spoofing of UDDI/ebXML Messages
    CAPEC-22 Exploiting Trust in Client
    CAPEC-23 File Content Injection
    CAPEC-230 Serialized Data with Nested Payloads
    CAPEC-231 Oversized Serialized Data Payloads
    CAPEC-24 Filter Failure through Buffer Overflow
    CAPEC-250 XML Injection
    CAPEC-261 Fuzzing for garnering other adjacent user/sensitive data
    CAPEC-267 Leverage Alternate Encoding
    CAPEC-28 Fuzzing
    CAPEC-3 Using Leading 'Ghost' Character Sequences to Bypass Input Filters
    CAPEC-31 Accessing/Intercepting/Modifying HTTP Cookies
    CAPEC-384 Application API Message Manipulation via Man-in-the-Middle
    CAPEC-385 Transaction or Event Tampering via Application API Manipulation
    CAPEC-386 Application API Navigation Remapping
    CAPEC-387 Navigation Remapping To Propagate Malicious Content
    CAPEC-388 Application API Button Hijacking
    CAPEC-42 MIME Conversion
    CAPEC-43 Exploiting Multiple Input Interpretation Layers
    CAPEC-45 Buffer Overflow via Symbolic Links
    CAPEC-46 Overflow Variables and Tags
    CAPEC-47 Buffer Overflow via Parameter Expansion
    CAPEC-473 Signature Spoof
    CAPEC-52 Embedding NULL Bytes
    CAPEC-53 Postfix, Null Terminate, and Backslash
    CAPEC-588 DOM-Based XSS
    CAPEC-63 Cross-Site Scripting (XSS)
    CAPEC-64 Using Slashes and URL Encoding Combined to Bypass Validation Logic
    CAPEC-664 Server Side Request Forgery
    CAPEC-665 Exploitation of Thunderbolt Protection Flaws
    CAPEC-67 String Format Overflow in syslog()
    CAPEC-7 Blind SQL Injection
    CAPEC-701 Browser in the Middle (BiTM)
    CAPEC-71 Using Unicode Encoding to Bypass Validation Logic
    CAPEC-72 URL Encoding
    CAPEC-73 User-Controlled Filename
    CAPEC-78 Using Escaped Slashes in Alternate Encoding
    CAPEC-79 Using Slashes in Alternate Encoding
    CAPEC-8 Buffer Overflow in an API Call
    CAPEC-80 Using UTF-8 Encoding to Bypass Validation Logic
    CAPEC-81 Web Server Logs Tampering
    CAPEC-83 XPath Injection
    CAPEC-85 AJAX Footprinting
    CAPEC-88 OS Command Injection
    CAPEC-9 Buffer Overflow in Local Command-Line Utilities

    Related CVEs

    CVE-2026-7168 (CVSS 5.3) — Successfully using libcurl to do a transfer over a specific HTTP proxy (`proxyA`) with **Digest** authenticati…
    CVE-2026-7009 (CVSS 5.3) — When curl is told to use the Certificate Status Request TLS extension, often referred to as *OCSP stapling*, t…
    CVE-2026-6429 (CVSS 5.3) — When asked to both use a `.netrc` file for credentials and to follow HTTP redirects, libcurl could leak the pa…
    CVE-2026-4873 (CVSS 5.9) — A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection …
    CVE-2026-6253 (CVSS 5.9) — curl might erroneously pass on credentials for a first proxy to a second proxy. This can happen when the foll…
    CVE-2026-5773 (CVSS 7.5) — libcurl might in some circumstances reuse the wrong connection for SMB(S) transfers. libcurl features a pool …
    CVE-2026-5545 (CVSS 6.5) — libcurl might in some circumstances reuse the wrong connection when asked to do an authenticated HTTP(S) reque…
    CVE-2026-6276 (CVSS 7.5) — Using libcurl, when a custom `Host:` header is first set for an HTTP request and a second request is subsequen…
    CVE-2026-3805 (CVSS 7.5) — When doing a second SMB request to the same host again, curl would wrongly use a data pointer pointing into al…
    CVE-2026-3784 (CVSS 6.5) — curl would wrongly reuse an existing HTTP proxy connection doing CONNECT to a server, even if the new request …

    References

    http://www.openwall.com/lists/oss-security/2024/03/27/4
    http://www.oracle.com/technetwork/security-advisory/cpuoct2018-4428296.html
    http://www.securityfocus.com/bid/90726
    http://www.securitytracker.com/id/1035907
    http://www.slackware.com/security/viewer.php?l=slackware-security&y=2016&m=slackware-security.495349
    https://curl.haxx.se/CVE-2016-3739.patch
    https://curl.haxx.se/changes.html#7_49_0
    https://curl.haxx.se/docs/adv_20160518.html
    https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05320149
    https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05390722
    https://security.gentoo.org/glsa/201701-47
    http://www.openwall.com/lists/oss-security/2024/03/27/4
    http://www.oracle.com/technetwork/security-advisory/cpuoct2018-4428296.html
    http://www.securityfocus.com/bid/90726
    http://www.securitytracker.com/id/1035907
    http://www.slackware.com/security/viewer.php?l=slackware-security&y=2016&m=slackware-security.495349
    https://curl.haxx.se/CVE-2016-3739.patch
    https://curl.haxx.se/changes.html#7_49_0
    https://curl.haxx.se/docs/adv_20160518.html
    https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05320149
    https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05390722
    https://security.gentoo.org/glsa/201701-47

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High