An out-of-bounds read flaw was found in the way Expat processed certain input. A remote attacker could send specially crafted XML that, when parsed by an application using the Expat library, would cause that application to crash or, possibly, execute arbitrary code with the permission of the user running the application.

A security regression for CVE-2019-9636 was discovered in python's functions urllib.parse.urlsplit and urllib.parse.urlparse, introduced with commit d537ab0ff9767ef024f26246899728f0116b1ec3. No upstream python version is affected by this regression but the vulnerable commit may already have been included downstream as part of the original fix for CVE-2019-9636.

Affected python versions ignore the user/password part before @ in the netloc component of a URL, thus it still allows an attacker to exploit the vulnerability as in CVE-2019-9636. Those functions do not properly handle URLs encoded with Punycode/Internationalizing Domain Names in Applications (IDNA), which may result in a wrong domain name (specifically the netloc component of URL - user@domain:port) being returned by those functions. When an application parses user-supplied URLs to store cookies, authentication credentials, or other kind of information, it is possible for an attacker to provide specially crafted URLs to make the application locate host-related information (e.g. cookies, authentication data) and send them to a different host than where it should, unlike if the URLs had been correctly parsed. The result of an attack may vary based on the application.

External Reference https://python-security.readthedocs.io/vuln/urlsplit-nfkc-normalization2.html

Vulnerable commit https://github.com/python/cpython/commit/d537ab0ff9767ef024f26246899728f0116b1ec3

Upstream patch https://github.com/python/cpython/commit/8d0ef0b5edeae52960c7ed05ae8a12388324f87e

A vulnerability was found in Python 2.7.x through 2.7.16 and 3.x through 3.7.2. An improper Handling of Unicode Encoding (with an incorrect netloc) during NFKC normalization could lead to an Information Disclosure (credentials, cookies, etc. that are cached against a given hostname) in the urllib.parse.urlsplit, urllib.parse.urlparse components. A specially crafted URL could be incorrectly parsed to locate cookies or authentication data and send that information to a different host than when parsed correctly.

References: https://bugs.python.org/issue36216 https://python-security.readthedocs.io/vuln/urlsplit-nfkc-normalization.html

Uptream Patch: https://github.com/python/cpython/pull/12201

A flaw was found in python. A stack-based buffer overflow was discovered in the ctypes module provided within Python. Applications that use ctypes without carefully validating the input passed to it may be vulnerable to this flaw, which would allow an attacker to overflow a buffer on the stack and crash the application. The highest threat from this vulnerability is to system availability.

Last updated 25 August 2025

A flaw was found in python. An improperly handled HTTP response in the HTTP client code of python may allow a remote attacker, who controls the HTTP server, to make the client script enter an infinite loop, consuming CPU time. The highest threat from this vulnerability is to system availability.

A flaw was found in python. In Lib/tarfile.py an attacker is able to craft a TAR archive leading to an infinite loop when opened by tarfile.open, because procpax lacks header validation.

A flaw was found in python's elementtree.c module, a wrapper for libexpat XML parser. xml.etree C accelerator don't call XMLSetHashSalt(), failing to properly initiate the random hash seed from a good CSPRNG source and making hash collision attacks with carefully crafted XML data easier.

Upstream bug:

https://bugs.python.org/issue34623.

A null pointer dereference vulnerability was found in the certificate parsing code in Python. This causes a denial of service to applications when parsing specially crafted certificates. This vulnerability is unlikely to be triggered if application enables SSL/TLS certificate validation and accepts certificates only from trusted root certificate authorities.

An issue was discovered in Python through 2.7.16, 3.x through 3.5.7, 3.6.x through 3.6.9, and 3.7.x through 3.7.4. The email module wrongly parses email addresses that contain multiple @ characters. An application that uses the email module and implements some kind of checks on the From/To headers of a message could be tricked into accepting an email address that should be denied. An attack may be the same as in CVE-2019-11340; however, this CVE applies to Python more generally.

libexpat. Multiple issues were addressed by updating to version 2.2.1

In libexpat before 2.2.8, crafted XML input could fool the parser into changing from DTD parsing to document parsing too early; a consecutive call to XMLGetCurrentLineNumber (or XMLGetCurrentColumnNumber) then resulted in a heap-based buffer over-read.

As reported on oss-security [1]:

So here are the CVE's for the two big ones, libxml2 and expat. Both are affected by the expansion of internal entities (which can be used to consume resources) and external entities (which can cause a denial of service against other services, be used to port scan, etc.).

To be clear:

==================== Internal entity expansion refers to the exponential/quadratic/fast linear expansion of XML entities, e.g.: ==================== <!DOCTYPE xmlbomb [ <!ENTITY a "1234567890" > <!ENTITY b "&a;&a;&a;&a;&a;&a;&a;&a;"> <!ENTITY c "&b;&b;&b;&b;&b;&b;&b;&b;"> <!ENTITY d "&c;&c;&c;&c;&c;&c;&c;&c;"> ]> <bomb>&d;</bomb>

or

<!DOCTYPE bomb [ <!ENTITY a "xxxxxxx... a couple of ten thousand chars"> ]> <bomb>&a;&a;&a;... repeat</bomb>

Which causes resources to be consumed

... Please use CVE-2013-0340 for expat internal entity expansion

[1] http://www.openwall.com/lists/oss-security/2013/02/22/4

An issue was discovered in urllib2 in Python 2.x through 2.7.16 and urllib in Python 3.x through 3.7.2. CRLF injection is possible if the attacker controls a url parameter, as demonstrated by the first argument to urllib.request.urlopen with \r\n followed by an HTTP header or a Redis command.

Reference: https://bugs.python.org/issue36276

An issue was discovered in urllib2 in Python 2.x through 2.7.16 and urllib in Python 3.x through 3.7.2. CRLF injection is possible if the attacker controls a url parameter, as demonstrated by the first argument to urllib.request.urlopen with \r\n (specifically in the path component of a URL) followed by an HTTP header or a Redis command. This is similar to CVE-2019-9740 query string issue.

Reference: https://bugs.python.org/issue35906

Last updated 25 August 2025

A CRLF injection flaw was discovered in python in the way URLs are handled when doing an HTTP/HTTPS connection (e.g. through urlopen() or HTTPConnection). An attacker who can control the url parameter passed to urlopen method in the urllib/urllib2 modules can inject CRLF sequences and HTTP headers by abusing the "host" part of the URL.

A reflected cross-site scripting (XSS) vulnerability was found in Python XML-RPC server. The servertitle field is not sufficiently sanitized allowing malicious JavaScript to be injected. Successful exploitation would allow a remote attacker to execute JavaScript code within the context of the affected user.

A vulnerability was found in Lib/ipaddress.py in Python through 3.8.3 improperly computes hash values in the IPv4Interface and IPv6Interface classes, which might allow a remote attacker to cause a denial of service if an application is affected by the performance of a dictionary containing IPv4Interface or IPv6Interface objects, and this attacker can cause many dictionary entries to be created.

References: https://bugs.python.org/issue41004 https://github.com/python/cpython/pull/20956

A flaw was found in Python 3's pydoc. This flaw allows a local or adjacent attacker who discovers or can convince another local or adjacent user to start a pydoc server to access the server and then use it to disclose sensitive information belonging to the other user that they would not normally have the ability to access. The highest threat from this vulnerability is to data confidentiality.

In Python (CPython) 3.6 through 3.6.10, 3.7 through 3.7.6, and 3.8 through 3.8.1, an insecure dependency load upon launch on Windows 7 may result in an attacker's copy of api-ms-win-core-path-l1-1-0.dll being loaded and used instead of the system's copy. Windows 8 and later are unaffected.

CVE-2018-20852 http.cookiejar.DefaultPolicy.domainreturnok in Lib/http/cookiejar.py in Python before 3.7.3 does not correctly validate the domain: it can be tricked into sending existing cookies to the wrong server. An attacker may abuse this flaw by using a server with a hostname that has another valid hostname as a suffix (e.g., pythonicexample.com to steal cookies for example.com). When a program uses http.cookiejar.DefaultPolicy and tries to do an HTTP connection to an attacker-controlled server, existing cookies can be leaked to the attacker. This affects 2.x through 2.7.16, 3.x before 3.4.10, 3.5.x before 3.5.7, 3.6.x before 3.6.9, and 3.7.x before 3.7.3. CVE-2014-4616 Array index error in the scanstring function in the json module in Python 2.7 through 3.5 and simplejson before 2.6.1 allows context-dependent attackers to read arbitrary process memory via a negative index value in the idx argument to the rawdecode function. CVE-2013-7040 Python 2.7 before 3.4 only uses the last eight bits of the prefix to randomize hash values, which causes it to compute hash values without restricting the ability to trigger hash collisions predictably and makes it easier for context-dependent attackers to cause a denial of service (CPU consumption) via crafted input to an application that maintains a hash table. NOTE: this vulnerability exists because of an incomplete fix for CVE-2012-1150.

A flaw was found in Python, specifically in the FTP (File Transfer Protocol) client library in PASV (passive) mode. The issue is how the FTP client trusts the host from the PASV response by default. This flaw allows an attacker to set up a malicious FTP server that can trick FTP clients into connecting back to a given IP address and port. This vulnerability could lead to FTP client scanning ports, which otherwise would not have been possible.