CVE-2026-27026: pypdf possibly has long runtimes for malformed FlateDecode streams
Impact
An attacker who uses this vulnerability can craft a PDF which leads to long runtimes. This requires a malformed /FlateDecode stream, where the byte-by-byte decompression is used.
Patches
This has been fixed in pypdf==6.7.1.
Workarounds
If you cannot upgrade yet, consider applying the changes from PR #3644.
Other sources
pypdf is a free and open-source pure-python PDF library. Prior to 6.7.1, an attacker who uses this vulnerability can craft a PDF which leads to long runtimes. This requires a malformed /FlateDecode stream, where the byte-by-byte decompression is used. This vulnerability is fixed in 6.7.1.
— NVD
Affected Software
Remediation
Patch Available
Event History
Frequently Asked Questions
What is the severity of CVE-2026-27026?
The severity of CVE-2026-27026 is moderate due to the potential for long runtimes caused by malformed FlateDecode streams.
How can I fix CVE-2026-27026?
To fix CVE-2026-27026, upgrade to pypdf version 6.7.1 or later.
What types of attacks can exploit CVE-2026-27026?
CVE-2026-27026 can be exploited by attackers using specially crafted PDFs that contain malformed FlateDecode streams.
Which software is affected by CVE-2026-27026?
CVE-2026-27026 affects the pypdf package prior to version 6.7.1.
What are the symptoms of CVE-2026-27026?
The symptoms of CVE-2026-27026 include significantly increased processing times when handling malformed PDFs.