The "stringprep" module didn't process characters from RFC 3454 tables B.2 or B.3 correctly: the latest Unicode codepoint attributes were used instead of the specified Unicode 3.2.0. This behavior would cause mismatches when processing domain names using IDNA 2003 (the "idna" codec) and the intableb2() function of the "stringprep" module. This only affects domain names containing characters that were not previously registered or had their Unicode attributes such as case-folding behavior updated since Unicode 3.2.0.

The HTTPPasswordMgr class in the urllib.request module, along with its subclasses HTTPPasswordMgrWithDefaultRealm and HTTPPasswordMgrWithPriorAuth, did not take the URL scheme into account when matching stored credentials against a requested URL. Credentials added for an https:// URL were also used for requests to the same host over http://, so an attacker able to redirect or downgrade a client to plain HTTP (for example, via an HTTPS-to-HTTP redirect or an on-path position) could capture credentials in cleartext. Credentials added for http:// URLs could likewise be sent over https://.

Credential matching is now scoped by URL scheme. Credentials registered with a URL that includes a scheme are only used for requests with the same scheme. Credentials registered with a bare authority (such as example.com or example.com:8080) continue to match any scheme, preserving compatibility with existing code, including proxy authentication.

Users who cannot upgrade immediately can mitigate by ensuring that applications never make plain http:// requests to hosts for which credentials are registered, for example by not following redirects to http:// URLs.

An issue was found in the CPython tempfile.TemporaryDirectory class affecting versions 3.12.1, 3.11.7, 3.10.13, 3.9.18, and 3.8.18 and prior.

The tempfile.TemporaryDirectory class would dereference symlinks during cleanup of permissions-related errors. This means users which can run privileged programs are potentially able to modify permissions of files referenced by symlinks in some circumstances.

https://github.com/python/cpython/commit/02a9259c717738dfe6b463c44d7e17f2b6d2cb3a https://github.com/python/cpython/commit/5585334d772b253a01a6730e8202ffb1607c3d25 https://github.com/python/cpython/commit/6ceb8aeda504b079fef7a57b8d81472f15cdd9a5 https://github.com/python/cpython/commit/81c16cd94ec38d61aa478b9a452436dc3b1b524d https://github.com/python/cpython/commit/8eaeefe49d179ca4908d052745e3bb8b6f238f82 https://github.com/python/cpython/commit/d54e22a669ae6e987199bb5d2c69bb5a46b0083b https://github.com/python/cpython/issues/91133 https://lists.debian.org/debian-lts-announce/2024/03/msg00025.html https://mail.python.org/archives/list/security-announce@python.org/thread/Q5C6ATFC67K53XFV4KE45325S7NS62LD/

-------- Forwarded Message -------- Subject: [Security-announce][CVE-2026-19672] tarfile extraction filter bypass allows creation of directories outside the destination Date: Wed, 19 Aug 2026 14:56:06 +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.

The tarfile module's tar and data extraction filters created directories outside the destination for members whose name leaves the destination and returns to it, such as ../evil/../dest/sub/file. The containment check used the resolved path, but intermediate directories were created from the name as given.

Only empty directories are created outside the destination. Member contents are still extracted inside it. To return to the destination the member's name must contain the destination directory's own final component, so extraction into a secure randomised directory is not affected.

This affects POSIX platforms only. On Windows, .. components are collapsed before the path reaches the filesystem, so the directories outside the destination are never created.

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

https://www.cve.org/CVERecord?id=CVE-2026-19672 https://github.com/python/cpython/pull/156000

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Last updated 6 July 2026

CPython >3.11 Insecure Input Validation resulting in privilege escalation

FTP PASV SSRF, ftpcp() does not use actual peer address, trusts server-supplied PASV host address

Last updated 6 July 2026

Incomplete control character validation in http.cookies

SourcelessFileLoader does not use io.opencode()

An issue was found in the CPython zipfile module affecting versions 3.12.1, 3.11.7, 3.10.13, 3.9.18, and 3.8.18 and prior.

The zipfile module is vulnerable to “quoted-overlap” zip-bombs which exploit the zip format to create a zip-bomb with a high compression ratio. The fixed versions of CPython makes the zipfile module reject zip archives which overlap entries in the archive.

https://github.com/python/cpython/commit/30fe5d853b56138dbec62432d370a1f99409fc85 https://github.com/python/cpython/commit/66363b9a7b9fe7c99eba3a185b74c5fdbf842eba https://github.com/python/cpython/commit/a2c59992e9e8d35baba9695eb186ad6c6ff85c51 https://github.com/python/cpython/commit/a956e510f6336d5ae111ba429a61c3ade30a7549 https://github.com/python/cpython/commit/d05bac0b74153beb541b88b4fca33bf053990183 https://github.com/python/cpython/commit/fa181fcf2156f703347b03a3b1966ce47be8ab3b https://github.com/python/cpython/issues/109858 https://lists.debian.org/debian-lts-announce/2024/03/msg00024.html https://lists.debian.org/debian-lts-announce/2024/03/msg00025.html https://mail.python.org/archives/list/security-announce@python.org/thread/XELNUX2L3IOHBTFU7RQHCY6OUVEWZ2FG/ https://www.bamsoftware.com/hacks/zipbomb/

Mitgation of CVE-2026-4519 was incomplete. If the URL contained "%action" the mitigation could be bypassed for certain browser types the "webbrowser.open()" API could have commands injected into the underlying shell. See CVE-2026-4519 for details.

https://www.cve.org/CVERecord?id=CVE-2026-15308 currently lists all versions before Python 3.15.0 as affected.

-------- Forwarded Message -------- Subject: [Security-announce][CVE-2026-15308] Incremental HTMLParser allows CPU-exhaustion DoS via repeated unterminated markup declarations Date: Thu, 9 Jul 2026 17:08:21 +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.

The incremental HTML parser (html.parser.HTMLParser) allows for CPU denial-of-service through repeated unterminated markup declarations when processing uncontrolled data.

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

https://www.cve.org/CVERecord?id=CVE-2026-15308 https://github.com/python/cpython/pull/153031

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-------- Forwarded Message -------- Date: Tue, 23 Jun 2026 16:55:19 +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 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-2026-11940 https://github.com/python/cpython/pull/151559

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CPython v3.12.0 alpha 7 was discovered to contain a heap use-after-free via the function asciidecode at /Objects/unicodeobject.c.

The CVE record currently lists versions "affected from 0 before 3.16.0"

-------- Forwarded Message -------- Subject: [Security-announce][CVE-2026-9669] bz2.BZ2Decompressor reuse after error can cause a stack buffer overflow Date: Mon, 8 Jun 2026 13:07:31 -0700 From: Emma Smith <emma () emmatyping dev> Reply-To: security-sig () python org To: security-announce () python org

There is a HIGH severity vulnerability affecting CPython.

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.

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

https://www.cve.org/CVERecord?id=CVE-2026-9669 https://github.com/python/cpython/pull/150600

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https://www.cve.org/CVERecord?id=CVE-2026-7774 currently lists affected versions as "from 0 before 3.15.0".

-------- Forwarded Message -------- Date: Thu, 4 Jun 2026 15:12:43 +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.

tarfile.datafilter could be bypassed using crafted link entries, including symlinks with empty or directory-like names, to redirect later archive members outside the intended extraction directory. This allowed a malicious tar archive to cause tarfile.extractall() to write files outside the destination directory, subject to the permissions of the extracting process.

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

https://www.cve.org/CVERecord?id=CVE-2026-7774 https://github.com/python/cpython/pull/149487

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-------- Forwarded Message -------- Date: Wed, 13 May 2026 20:15:52 +0000 From: Seth Larson <seth () python org> Reply-To: security-sig () python org To: security-announce () python org

There is a MEDIUM severity vulnerability affecting CPython. Please see the linked CVE ID for the latest information on affected versions:

https://www.cve.org/CVERecord?id=CVE-2026-8328 https://github.com/python/cpython/pull/149648

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On 5/11/26 19:20, Alan Coopersmith wrote: This sentence ^^ deserves additional highlight. I confirm.

https://www.cve.org/CVERecord?id=CVE-2026-5713 provides additional details on the affected versions: 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. ------- Forwarded Message -------- Date: Tue, 14 Apr 2026 15:13:09 +0000 From: Seth Larson <seth () python org> Reply-To: security-sig () python org To: security-announce () python org

There is a MEDIUM severity vulnerability affecting CPython. Please see the linked CVE ID for the latest information on affected versions:

https://www.cve.org/CVERecord?id=CVE-2026-5713 https://github.com/python/cpython/pull/148187

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-------- Forwarded Message -------- Date: Mon, 13 Apr 2026 21:53:53 +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.

Mitgation of CVE-2026-4519 was incomplete. If the URL contained "%action" the mitigation could be bypassed for certain browser types the "webbrowser.open()" API could have commands injected into the underlying shell. See CVE-2026-4519 for details.

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

https://www.cve.org/CVERecord?id=CVE-2026-4786 https://github.com/python/cpython/pull/148170

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-------- Forwarded Message -------- Subject: [Security-announce][CVE-2026-6100] Use-after-free in lzma.LZMADecompressor, bz2.BZ2Decompressor, and gzip.GzipFile after re-use under memory pressure Date: Mon, 13 Apr 2026 17:13:40 +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.

Use-after-free (UAF) was possible in the lzma.LZMADecompressor, bz2.BZ2Decompressor, and gzip.GzipFile when a memory allocation fails with a MemoryError and the decompression instance is re-used. This scenario can be triggered if the process is under memory pressure. The fix cleans up the dangling pointer in this specific error condition.

The vulnerability is only present if the program re-uses decompressor instances across multiple decompression calls even after a MemoryError is raised during decompression. Using the helper functions to one-shot decompress data such as lzma.decompress(), bz2.decompress(), gzip.decompress(), and zlib.decompress() are not affected as a new decompressor instance is created for each call. If the decompressor instance is not re-used after an error condition, this usage is similarly not vulnerable.

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

https://www.cve.org/CVERecord?id=CVE-2026-6100 https://github.com/python/cpython/pull/148396

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-------- Forwarded Message -------- Date: Fri, 10 Apr 2026 17:51:54 +0000 From: Seth Larson <seth () python org> Reply-To: security-sig () python org To: security-announce () python org

There is a MEDIUM severity vulnerability affecting CPython.

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

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

https://www.cve.org/CVERecord?id=CVE-2026-1502 https://github.com/python/cpython/pull/146212

-------- Forwarded Message -------- Date: Fri, 20 Mar 2026 15:03:34 +0000 From: Seth Larson <seth () python org> Reply-To: security-sig () python org To: security-announce () python org

There is a MEDIUM severity vulnerability affecting CPython. Please see the linked CVE ID for the latest information on affected versions:

https://www.cve.org/CVERecord?id=CVE-2026-4519 https://github.com/python/cpython/pull/143931 Security-announce mailing list -- security-announce () python org https://mail.python.org/mailman3//lists/security-announce.python.org

A vulnerability has been found in the CPython venv module and CLI where path names provided when creating a virtual environment were not quoted properly, allowing the creator to inject commands into virtual environment "activation" scripts (ie "source venv/bin/activate"). This means that attacker-controlled virtual environments are able to run commands when the virtual environment is activated. Virtual environments which are not created by an attacker or which aren't activated before being used (ie "./venv/bin/python") are not affected.