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    CVE-2021-29921

    In Python before 3,9,5, the ipaddress library mishandles leading zero characters in the octets of an IP address string. This (in some situations) allows attackers to bypass access control that is based on IP addresses.

    Published:Apr 30, 2021
    Last Modified:Nov 3, 2025
    EPS:May 6, 2021
    EPSS Score:0.01651
    CVSS Score:9.8

    Affected Products

    Vendor
    Oracle
    Product
    Communications Cloud Native Core Automated Test Suite
    Vendor
    Oracle
    Product
    Communications Cloud Native Core Binding Support Function
    Vendor
    Oracle
    Product
    Communications Cloud Native Core Network Slice Selection Function
    Vendor
    Oracle
    Product
    Graalvm
    Vendor
    Oracle
    Product
    Zfs Storage Appliance Kit
    Vendor
    Python
    Product
    Python
    Vendor
    Redhat
    Product
    Enterprise Linux
    Vendor
    Redhat
    Product
    Rhel Software Collections

    Exploits

    https://github.com/sickcodes/security/blob/master/advisories/SICK-2021-014.mdhttps://sick.codes/sick-2021-014https://github.com/sickcodes/security/blob/master/advisories/SICK-2021-014.mdhttps://sick.codes/sick-2021-014

    Common Weakness Enumeration

    CWE-20 Improper Input Validation

    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-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-153 Input Data Manipulation
    CAPEC-182 Flash Injection
    CAPEC-209 XSS Using MIME Type Mismatch
    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-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-67 String Format Overflow in syslog()
    CAPEC-7 Blind SQL Injection
    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

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    CVE-2021-43859 (CVSS 7.5) — XStream is an open source java library to serialize objects to XML and back again. Versions prior to 1.4.19 ma…
    CVE-2022-20614 (CVSS 4.3) — A missing permission check in Jenkins Mailer Plugin 391.ve4a_38c1b_cf4b_ and earlier allows attackers with Ove…
    CVE-2022-20612 (CVSS 4.3) — A cross-site request forgery (CSRF) vulnerability in Jenkins 2.329 and earlier, LTS 2.319.1 and earlier allows…
    CVE-2022-20615 (CVSS 5.4) — Jenkins Matrix Project Plugin 1.19 and earlier does not escape HTML metacharacters in node and label names, an…
    CVE-2022-20613 (CVSS 4.3) — A cross-site request forgery (CSRF) vulnerability in Jenkins Mailer Plugin 391.ve4a_38c1b_cf4b_ and earlier al…
    CVE-2021-39147 (CVSS 8.5) — XStream is a simple library to serialize objects to XML and back again. In affected versions this vulnerabilit…
    CVE-2021-39150 (CVSS 8.5) — XStream is a simple library to serialize objects to XML and back again. In affected versions this vulnerabilit…
    CVE-2021-39148 (CVSS 8.5) — XStream is a simple library to serialize objects to XML and back again. In affected versions this vulnerabilit…

    References

    https://bugs.python.org/issue36384
    https://docs.python.org/3/library/ipaddress.html
    https://github.com/python/cpython/blob/63298930fb531ba2bb4f23bc3b915dbf1e17e9e1/Misc/NEWS.d/3.8.0a4.rst
    https://github.com/python/cpython/pull/12577
    https://github.com/python/cpython/pull/25099
    https://github.com/sickcodes
    https://github.com/sickcodes/security/blob/master/advisories/SICK-2021-014.md
    https://python-security.readthedocs.io/vuln/ipaddress-ipv4-leading-zeros.html
    https://security.gentoo.org/glsa/202305-02
    https://security.netapp.com/advisory/ntap-20210622-0003/
    https://sick.codes/sick-2021-014
    https://www.oracle.com//security-alerts/cpujul2021.html
    https://www.oracle.com/security-alerts/cpuapr2022.html
    https://www.oracle.com/security-alerts/cpujan2022.html
    https://www.oracle.com/security-alerts/cpujul2022.html
    https://www.oracle.com/security-alerts/cpuoct2021.html
    https://bugs.python.org/issue36384
    https://docs.python.org/3/library/ipaddress.html
    https://github.com/python/cpython/blob/63298930fb531ba2bb4f23bc3b915dbf1e17e9e1/Misc/NEWS.d/3.8.0a4.rst
    https://github.com/python/cpython/pull/12577
    https://github.com/python/cpython/pull/25099
    https://github.com/sickcodes
    https://github.com/sickcodes/security/blob/master/advisories/SICK-2021-014.md
    https://lists.debian.org/debian-lts-announce/2024/12/msg00000.html
    https://python-security.readthedocs.io/vuln/ipaddress-ipv4-leading-zeros.html
    https://security.gentoo.org/glsa/202305-02
    https://security.netapp.com/advisory/ntap-20210622-0003/
    https://sick.codes/sick-2021-014
    https://www.oracle.com//security-alerts/cpujul2021.html
    https://www.oracle.com/security-alerts/cpuapr2022.html
    https://www.oracle.com/security-alerts/cpujan2022.html
    https://www.oracle.com/security-alerts/cpujul2022.html
    https://www.oracle.com/security-alerts/cpuoct2021.html

    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