Vulnerability PYSEC-2026-4156
Unknown
UNKNOWN RISK
Vulnerabilities without an assigned CVSS score. Severity is not determinable from available data.
20 days ago
October 01, 2026 at 04:44 PM UTC
pypdf: Possible long runtimes for partially malformed FlateDecode streams (Follow-up)
1.0 - 6.18.0
1.0 - 6.18.0
Summary
pypdf: Possible long runtimes for partially malformed FlateDecode streams (Follow-up)
Details
Impact
An attacker who uses this vulnerability can craft a PDF which leads to long runtimes. This requires a partially malformed /FlateDecode stream, where the byte-by-byte decompression is used.
Patches
This has been fixed in pypdf==6.18.1.
Workarounds
If you cannot upgrade yet, consider applying the changes from PR #4073.
Related Vulnerabilities
Other vulnerabilities affecting the same packages
Medium Risk
1 hour ago
pypdf: Possible infinite loop in PdfWriter.find_outline_item
1.0 - 6.20.0 GHSA-qfv9-64jg-mh7p
1.0 - 6.20.0 GHSA-qfv9-64jg-mh7p
Medium Risk
1 hour ago
pypdf: Possible infinite loop when removing tree items
1.0 - 6.20.0 GHSA-9mx8-4j7g-633p
1.0 - 6.20.0 GHSA-9mx8-4j7g-633p
Medium Risk
2 hours ago
pypdf: Possible infinite loop when hitting EOF in standard xref table
1.0 - 6.19.0 GHSA-39mj-jf6j-2qj3
1.0 - 6.19.0 GHSA-39mj-jf6j-2qj3
Medium Risk
2 hours ago
pypdf: Possible large memory usage for streams with multiple filters
1.0 - 6.19.0 GHSA-7mh2-4gg2-979f
1.0 - 6.19.0 GHSA-7mh2-4gg2-979f
Unknown
20 days ago
pypdf: Possible long runtimes when generating appearance streams
1.0 - 6.18.1 PYSEC-2026-4157
1.0 - 6.18.1 PYSEC-2026-4157
Impacted packages
Timeline
Published
20 days ago
October 01, 2026 at 04:44 PM UTC
Fixed (6.18.1)
1 month ago
September 11, 2026 at 10:10 AM UTC
Last Modified
20 days ago
October 01, 2026 at 05:45 PM UTC