CVE-2026-22691 pypdf has possible long runtimes for malformed startxref
Attackers can cause denial of service via long runtimes when processing malformed PDFs with excessive whitespace in non-strict mode.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-22691?
CVE-2026-22691 is a low-severity denial of service vulnerability in Pypdf Project Pypdf, published on 10 Jan 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 version 6.6.0, pypdf has possible long runtimes for malformed startxref. An attacker who uses this vulnerability can craft a PDF which leads to possibly long runtimes for invalid startxref entries. When rebuilding the cross-reference table, PDF files with lots of whitespace characters become problematic. Only the non-strict reading mode is affected. Only the non-strict reading mode is affected. This issue has been patched in version 6.6.0.
Which versions are affected by CVE-2026-22691?
3 open source packages ship an affected version, including pypdf. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
pypdf PyPI | All versions | 6.6.0 |
pypdf PyPI | All versions | 6.6.0 |
pypdf PyPI | All versions | 6.6.0 |
Products include Pypdf Project Pypdf.
How do I fix CVE-2026-22691?
Upgrade pypdf to 6.6.0 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-2026-22691 being exploited?
There is no known exploitation of CVE-2026-22691 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-2026-102997 pypdf: Possible long runtimes for partially malformed FlateDecode streams (Follow-up)
Sources
Also known as DEBIAN-CVE-2026-22691, GHSA-4f6g-68pf-7vhv, PYSEC-2026-1828, UBUNTU-CVE-2026-22691.