CVE-2026-102997 pypdf: Possible long runtimes for partially malformed FlateDecode streams (Follow-up)
A crafted PDF with malformed FlateDecode streams causes inefficient decompression, leading to long runtimes and application unavailability in pypdf.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-102997?
CVE-2026-102997 is a high-severity denial of service vulnerability in Pypdf Project Pypdf, published on 30 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-102997?
3 open source packages ship an affected version, including pypdf. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
pypdf PyPI | All versions | 6.18.1 |
pypdf PyPI | All versions | 6.18.1 |
pypdf PyPI | All versions | 6.18.1 |
Products include Pypdf Project Pypdf.
How do I fix CVE-2026-102997?
Upgrade pypdf to 6.18.1 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-102997 being exploited?
There is no known exploitation of CVE-2026-102997 in the wild and no public exploit code.
Other vulnerabilities in Pypdf Project Pypdf
- CVE-2026-102993 pypdf: Possible large memory usage when retrieving Roman page labels
- CVE-2026-102994 pypdf: Possible long runtimes/large memory usage when parsing indirect objects
- CVE-2026-102995 pypdf: Possible large memory usage for large /ToUnicode streams (Follow-up 2)
- CVE-2026-102996 pypdf: Possible large memory usage when parsing font data
- CVE-2026-102998 pypdf: Possible long runtimes when generating appearance streams
Sources
Also known as DEBIAN-CVE-2026-102997, ECHO-c89a-8658-9f90, GHSA-jw7q-gvrg-4vj3, MINI-2846-w54j-rj32, MINI-2c27-fr28-wxqh, MINI-4fg8-x339-8p8w and 14 more.