High severity · published Sep 30, 2026
CVE-2026-102997
pypdf: Possible long runtimes for partially malformed FlateDecode streams (Follow-up)
7.5
CVSS
0.3%
EPSS
No
On KEV
Description
pypdf is a free and open-source pure-python PDF library. Prior to 6.18.1, a crafted PDF containing a partially malformed /FlateDecode stream with padded data can force pypdf/filters.py to use inefficient byte-by-byte decompression while the earlier recovery counter fails to advance for bytes that successfully decode, causing long runtimes and application unavailability. This is a residual issue after the malformed FlateDecode recovery fix. This issue is fixed in version 6.18.1.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 27% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
PY
pypdf · py-pdf
< 6.18.1 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-102997
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-102997
x_refsource_CONFIRM
https://github.com/py-pdf/pypdf/security/advisories/GHSA-jw7q-gvrg-4vj3
x_refsource_MISC
https://github.com/py-pdf/pypdf/pull/4073
x_refsource_MISC
https://github.com/py-pdf/pypdf/commit/d9d38cf99b115deb562d3b68f36c33027bc04f79
x_refsource_MISC
https://github.com/py-pdf/pypdf/releases/tag/6.18.1
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