Python vulnerabilities

Python versions before 3.3.4 RC1 allow remote attackers to cause a denial of service via a file size value larger than the size of the zip file in functions related to reading and extracting zip files.

The email module in Python through 3.11.3 incorrectly parses email addresses containing special characters. The wrong portion of an RFC2822 header is identified as the value of the addr-spec.

A vulnerability in the urllib.parse component of Python before version 3.11.4 allows attackers to bypass blocklisting methods by supplying a URL that starts with blank characters.

The email module in Python, specifically the BytesGenerator class, improperly quotes newlines in email headers during serialization, allowing header injection. This only affects usage of LiteralHeader that does not respect email folding.

A flaw was found in Python's urllib.parse module where the urlparse method does not sanitize input, allowing characters like ' ' and ' ' in the URL path. This can lead to CRLF injection attacks.

A vulnerability in Python 3.9.x before 3.9.16 and 3.10.x before 3.10.9 on Linux allows local privilege escalation in a non-default configuration. The multiprocessing library with the forkserver start method permits pickle deserialization from any user on the same local network of the machine.

When decompressing crafted zip files using the bzip/LZMA/Zstandard compressions, Python could use an attacker-controlled size to pre-allocate memory, possibly resulting in memory exhaustion.

The 'stringprep' module did not 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 causes mismatches when processing domain names using IDNA 2003 (the 'idna' codec) and the in_table_b2() 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.

A vulnerability in Python's csv.Sniffer where attacker-controlled CSV samples can trigger super-linear regular-expression work during dialect sniffing, consuming significant CPU.

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

CVE-2026-12003 vulnerability concerns how Python handles the VPATH variable during builds from the source tree. On Windows, VPATH may point to a location outside the Python installation directory, potentially allowing low-privilege users to create files that could be used to access an alternative `Lib` folder.

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.

The tarfile.data_filter function in Python can be bypassed using crafted symlinks, allowing files to be written outside the target directory during tar extraction. An attacker can place files in arbitrary locations.

The unicodedata.normalize() function can consume 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.

Vulnerability in the ftpcp() function in Python's ftplib.py module. This function was not updated when CVE-2021-4189 was fixed, allowing an attacker to control the IP address and port passed to target.sendport().

The sock_recvfrom_into() method in asyncio.ProactorEventLoop (Windows only) lacked a boundary check for the data buffer when using the nbytes parameter, allowing an out-of-bounds buffer write if data was larger than the buffer size.

A use-after-free vulnerability was found in Python's standard library in `lzma.LZMADecompressor`, `bz2.BZ2Decompressor`, and `gzip.GzipFile`. It occurs when a memory allocation fails with a `MemoryError` and the decompressor instance is reused. The fix cleans up the dangling pointer in this specific error condition.

The webbrowser.open() API in Python would accept URLs starting with dashes, which could be interpreted as command line options by certain web browsers. The new behavior rejects such URLs.

The Python standard library functions `urllib.parse.urlsplit` and `urlparse` accept domain names with square brackets, which is invalid per RFC 3986. Square brackets are only meant as delimiters for IPv6 and IPvFuture hosts. This can cause differential parsing between Python's URL parser and other compliant parsers.

An issue was discovered in Python before 3.8.18, 3.9.x before 3.9.18, 3.10.x before 3.10.13, and 3.11.x before 3.11.5, affecting servers using TLS client authentication. If a TLS server-side socket is closed quickly, data may still be readable from the socket buffer without authentication.