pypdf: Possible infinite loop when cloning dictionaries
Affects pypdf versions before 6.21.4 where code clones or duplicates a DictionaryObject. Fixed in pypdf 6.21.4.
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- Fix
- Fixed in 6.21.4
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: yes
- Technical impact: partial
Summary
pypdf, a free and open-source pure-Python library for working with PDF files, is affected by this vulnerability. A specially crafted PDF with a cyclic dictionary structure can cause the library to hang in an infinite loop when it copies or duplicates that content, which can stall the application using it.
Summarized by anthropic/claude-haiku-5.5. Verify details against the original sources.
Read the original description
pypdf is a free and open-source pure-python PDF library. Prior to 6.21.4, pypdf can enter an infinite loop when cloning or duplicating a crafted cyclic DictionaryObject. Clone traversal checked generated destination references rather than the original source references, allowing some source cycles to evade the visited-object check. This issue is fixed in version 6.21.4.
Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: none · Automatable: yes · Technical impact: partial
- Record last updated
Affected versions
- py-pdf pypdf
fixed in 6.21.4
References 4
GitHub · py-pdf/pypdf
Questions about CVE-2026-119205
What does this mean?
A crafted PDF can make pypdf enter an infinite loop when it clones a cyclic dictionary, which causes a denial of service.Source: github.com
Am I affected, and how do I check?
The advisory lists pypdf releases before 6.21.4 as affected. The bug only triggers when code clones or duplicates a DictionaryObject; check the installed version with pip show pypdf.Source: github.com
What should I do about it?
Upgrade to pypdf 6.21.4 or later, which contains the fix. The listed workaround is to apply the changes from PR #4288.Source: github.com
Is it being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data