There is a defect in the CPython standard library module “mimetypes” where on Windows the default list of known file locations are writable meaning other users can create invalid files to cause MemoryError to be raised on Python runtime startup or have file extensions be interpreted as the incorrect file type.

This defect is caused by the default locations of Linux and macOS platforms (such as “/etc/mime.types”) also being used on Windows, where they are user-writable locations (“C:\etc\mime.types”).

To work-around this issue a user can call mimetypes.init() with an empty list (“[]”) on Windows platforms to avoid using the default list of known file locations.

ssl.SSLContext.wrapbio() didn't require the serverhostname argument to not be None if ssl.SSLContext.checkhostname was set. Due to a missing parameter check in SSLObject, if the serverhostname argument isn't supplied then hostname verification would be silently skipped.

This defect could lead to programs where certificate hostname verification appeared to be succeeding with SSLContext.checkhostname = True and no ValueError being raised due to misconfiguration.

If the program passes a serverhostname value that isn't an empty string or None to any of these APIs then certificate hostname verification proceeds as expected and the program is not affected by this vulnerability.

Mitigating this vulnerability doesn't require updating Python or applying the patch. To mitigate, pass a valid non-None and non-empty serverhostname value to SSLContext.wrapbio(), asyncio.createconnection(), or asyncio.loop.starttls() and certificate hostname verification will proceed as expected. Upgrading to the latest version of Python or applying the patch only changes the behavior from silently skipping hostname verification to raising a ValueError, similar to SSLContext.wrapsocket(), when serverhostname isn't supplied.

Race condition in tempfile.TemporaryDirectory cleanup allows deleting files outside the temporary directory

End of life: 10/31/2031, End of support: 10/9/2028, Latest version: 3.15.0

A remote, unauthenticated TLS client can make a server crash or call through a freed pointer if its snicallback assigns a different context to SSLSocket.context (the documented way to select a certificate per server name) and nothing else keeps the original ssl.SSLContext alive. Typical cases are servers that create an SSLContext per connection or replace it while connections are open; servers that wrap their listening socket with it are not affected.

Mitigation: keep a reference to every SSLContext that sets snicallback for the lifetime of the server. TLS clients are not affected.

xml.parsers.expat and xml.etree.ElementTree use insufficient entropy for Expat hash-flooding protection, which allows a crafted XML document to trigger hash flooding.\r\n\r\nFully mitigating this vulnerability requires both updating libexpat to 2.8.0 or later and applying this patch.

-------- Forwarded Message -------- Date: Wed, 30 Sep 2026 16:10:08 +0000 From: Seth Larson <seth () python org> Reply-To: security-sig () python org To: security-announce () python org

There is a CRITICAL severity vulnerability affecting CPython.

Please see the linked CVE ID for the latest information on affected versions:

https://www.cve.org/CVERecord?id=CVE-2026-19445 https://github.com/python/cpython/pull/158504

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-------- Forwarded Message -------- Date: Wed, 30 Sep 2026 16:08:09 +0000 From: Seth Larson <seth () python org> Reply-To: security-sig () python org To: security-announce () python org

There is a HIGH severity vulnerability affecting CPython.

Please see the linked CVE ID for the latest information on affected versions:

https://www.cve.org/CVERecord?id=CVE-2026-19553 https://github.com/python/cpython/pull/158503 Security-announce mailing list -- security-announce () python org https://mail.python.org/mailman3//lists/security-announce.python.org

Summary

In the fallback extraction path for source distributions, pip used Python’s tarfile module without verifying that symbolic/hard link targets resolve inside the intended extraction directory. A malicious sdist can include links that escape the target directory and overwrite arbitrary files on the invoking host during pip install.

Impact

Successful exploitation enables arbitrary file overwrite outside the build/extraction directory on the machine running pip. This can be leveraged to tamper with configuration or startup files and may lead to further code execution depending on the environment, but the direct, guaranteed impact is integrity compromise on the vulnerable system.

Conditions

The issue is triggered when installing an attacker-controlled sdist (e.g., from an index or URL) and the fallback extraction code path is used. No special privileges are required beyond running pip install; active user action is necessary.

Remediation

The fix, while available as a patch that can be manually applied, has not yet been put into a numbered version but is planned for 25.3. Using a Python interpreter that implements the safe-extraction behavior described by PEP 706 provides additional defense in depth for other tarfile issues but is not a substitute for upgrading pip for this specific flaw.

Summary A path traversal vulnerability in PackageIndex was fixed in setuptools version 78.1.1

Details def downloadurl(self, url, tmpdir): # Determine download filename # name, fragment = egginfoforurl(url) if name: while '..' in name: name = name.replace('..', '.').replace('\\', '') else: name = "downloaded" # default if URL has no path contents

if name.endswith('.egg.zip'): name = name[:-4] # strip the extra .zip before download

--> filename = os.path.join(tmpdir, name)

Here: https://github.com/pypa/setuptools/blob/6ead555c5fb29bc57fe6105b1bffc163f56fd558/setuptools/packageindex.py#L810C1-L825C88

os.path.join() discards the first argument tmpdir if the second begins with a slash or drive letter. name is derived from a URL without sufficient sanitization. While there is some attempt to sanitize by replacing instances of '..' with '.', it is insufficient.

Risk Assessment As easyinstall and packageindex are deprecated, the exploitation surface is reduced. However, it seems this could be exploited in a similar fashion like https://github.com/advisories/GHSA-r9hx-vwmv-q579, and as described by POC 4 in https://github.com/advisories/GHSA-cx63-2mw6-8hw5 report: via malicious URLs present on the pages of a package index.

Impact An attacker would be allowed to write files to arbitrary locations on the filesystem with the permissions of the process running the Python code, which could escalate to RCE depending on the context.

References https://huntr.com/bounties/d6362117-ad57-4e83-951f-b8141c6e7ca5 https://github.com/pypa/setuptools/issues/4946

Out-of-memory when loading Plist

setuptools is a package that allows users to download, build, install, upgrade, and uninstall Python packages. A path traversal vulnerability in PackageIndex is present in setuptools prior to version 78.1.1. An attacker would be allowed to write files to arbitrary locations on the filesystem with the permissions of the process running the Python code, which could escalate to remote code execution depending on the context. Version 78.1.1 fixes the issue.

There is a MEDIUM severity vulnerability affecting CPython.

The email module didn’t properly quote newlines for email headers when serializing an email message allowing for header injection when an email is serialized.

Last updated 6 July 2026

Last updated 6 July 2026

Incomplete mitigation of CVE-2026-4519, %action expansion for command injection to webbrowser.open()

bz2.BZ2Decompressor objects could be reused after a decompression error. If an application caught the resulting OSError and retried with the same decompressor, crafted input could cause the decompressor to resume from an invalid internal state and perform out-of-bounds writes to a stack buffer. This could crash the process when processing untrusted data.

Potential DoS via quadratic complexity in unicodedata.normalize()

Improper validation of IPv6 and IPvFuture addresses

CR/LF bytes were not rejected by HTTP client proxy tunnel headers or host.

Last updated 6 July 2026

Last updated 24 March 2025

There is a defect in the CPython “tarfile” module affecting the “TarFile” extraction and entry enumeration APIs. The tar implementation would process tar archives with negative offsets without error, resulting in an infinite loop and deadlock during the parsing of maliciously crafted tar archives.

This vulnerability can be mitigated by including the following patch after importing the “tarfile” module:

import tarfile

def blockpatched(self, count): if count < 0: # pragma: no cover raise tarfile.InvalidHeaderError("invalid offset") return blockpatched.origblock(self, count)

blockpatched.origblock = tarfile.TarInfo.block tarfile.TarInfo.block = blockpatched

The "profiling.sampling" module (Python 3.15+) and "asyncio introspection capabilities" (3.14+, "python -m asyncio ps" and "python -m asyncio pstree") features could be used to read and write addresses in a privileged process if that process connected to a malicious or "infected" Python process via the remote debugging feature. This vulnerability requires persistently and repeatedly connecting to the process to be exploited, even after the connecting process crashes with high likelihood due to ASLR.

The fix for CVE-2026-0672, which rejected control characters in http.cookies.Morsel, was incomplete. The Morsel.update(), |= operator, and unpickling paths were not patched, allowing control characters to bypass input validation. Additionally, BaseCookie.jsoutput() lacked the output validation applied to BaseCookie.output().

The import hook in CPython that handles legacy .pyc files (SourcelessFileLoader) is incorrectly handled in FileLoader (a base class) and so does not use io.opencode() to read the .pyc files. sys.audit handlers for this audit event therefore do not fire.

A flaw was found in the Python tarfile module. Extracting a crafted TAR archive with the tarfile.extract or tarfile.extractall functions could lead to a directory traversal vulnerability, resulting in overwrite of arbitrary files.

-------- Forwarded Message -------- Date: Tue, 16 Jun 2026 16:01:03 +0100 From: Steve Dower <steve.dower () python org> Reply-To: security-sig () python org To: security-announce () python org

Reported by Jake Yamaki, Senior Consultant, Bishop Fox.

Please see the linked CVE ID for the latest information on affected versions:

https://www.cve.org/CVERecord?id=CVE-2026-12003 https://github.com/python/cpython/pull/151545 Security-announce mailing list -- security-announce () python org https://mail.python.org/mailman3//lists/security-announce.python.org

-------- Forwarded Message -------- Date: Wed, 3 Jun 2026 14:56:33 +0100 From: Stan Ulbrych via Security-announce <security-announce () python org> Reply-To: security-sig () python org To: security-announce () python org CC: Stan Ulbrych <stanulbrych () gmail com>

There is a MEDIUM severity vulnerability affecting CPython.

unicodedata.normalize() can take excessive CPU time when processing specially crafted Unicode input containing long runs of combining characters with alternating Canonical Combining Class values. This affects all normalization forms.

Please see the linked CVE ID for the latest information on affected versions:

https://www.cve.org/CVERecord?id=CVE-2026-3276 https://github.com/python/cpython/pull/149080

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A Denial of Service (DoS) vulnerability exists in the jaraco/zipp library, affecting all versions prior to 3.19.1. The vulnerability is triggered when processing a specially crafted zip file that leads to an infinite loop. This issue also impacts the zipfile module of CPython, as features from the third-party zipp library are later merged into CPython, and the affected code is identical in both projects. The infinite loop can be initiated through the use of functions affecting the Path module in both zipp and zipfile, such as joinpath, the overloaded division operator, and iterdir. Although the infinite loop is not resource exhaustive, it prevents the application from responding. The vulnerability was addressed in version 3.19.1 of jaraco/zipp.