VulnerabilityPublished 27 Jan 2026

CVE-2026-24688: py-pdf pypdf · Infinite Loop

Affects py-pdf pypdfSource CVE Database V5

Not known to be exploited · CVSS 5.1 Medium : upgrade to 6.6.2 when convenient.

Data as of 26 Oct 2026, 11:42 UTC

CVSS 4.0 base score

5.1Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.4% chance of exploitation in 30 days – higher than 38% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 6.6.2

CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Attack Vector: Local
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: Low
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable system is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or through terminal emulation (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 27 Jan 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade py-pdf pypdf to 6.6.2.

Affected software

Product	Affected	Fixed in
py-pdfpypdf	Affected <6.6.2	Fixed in 6.6.2
PyPIpypdf`pkg:pypi/pypdf`Other threats	Affected <6.6.2	Fixed in 6.6.2

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

European organizations should prioritize upgrading all instances of pypdf to version 6.6.2 or later to fully remediate the vulnerability. If immediate upgrading is not possible due to compatibility or operational constraints, applying the patch from pull request #3610 manually is recommended to fix the infinite loop condition. Additionally, organizations should implement input validation and sandboxing for PDF processing workflows to limit the impact of malicious PDFs. Rate limiting and resource usage monitoring on services handling PDFs can help detect and mitigate denial of service attempts. Employing application-level timeouts or watchdog mechanisms to terminate processes stuck in infinite loops can reduce service disruption. Regularly auditing software dependencies and maintaining an up-to-date inventory of pypdf usage across internal and external applications will aid in comprehensive mitigation. Finally, educating developers and system administrators about this vulnerability will ensure timely patching and response.

Description

### Impact An attacker who uses this vulnerability can craft a PDF which leads to an infinite loop. This requires accessing the outlines/bookmarks. ### Patches This has been fixed in [pypdf 6.6.2](https://github.com/py-pdf/pypdf/releases/tag/6.6.2). ### Workarounds If projects cannot upgrade yet, consider applying the changes from PR [#3610](https://github.com/py-pdf/pypdf/pull/3610).

Impact

For European organizations, the primary impact of CVE-2026-24688 is the risk of denial of service in applications or services that utilize vulnerable versions of pypdf to process PDF documents. This could affect document management systems, automated PDF processing pipelines, web applications allowing PDF uploads, or any internal tools relying on pypdf. Disruption of these services could lead to operational downtime, reduced productivity, and potential reputational damage, especially in sectors heavily reliant on document workflows such as finance, legal, healthcare, and government. While the vulnerability does not directly compromise confidentiality or integrity, the availability impact could be significant if exploited at scale or in critical environments. The lack of known exploits reduces immediate risk, but the ease of crafting malicious PDFs means attackers could weaponize this vulnerability in targeted attacks or spam campaigns. European organizations with strict uptime requirements or regulatory obligations around service availability should consider this vulnerability a moderate threat.

Summary

CVE-2026-24688 is a vulnerability classified under CWE-835 (Loop with Unreachable Exit Condition) affecting the pypdf library, a widely used pure-Python PDF processing tool. Versions of pypdf prior to 6.6.2 contain a flaw in the handling of PDF outlines/bookmarks, where a specially crafted PDF can cause the library to enter an infinite loop. This infinite loop results from a logic error in the iteration or parsing of the outline structure, preventing normal termination of the loop. The consequence is a denial of service (DoS) condition, as the process consuming the PDF becomes unresponsive or consumes excessive CPU resources. The vulnerability does not require any privileges or user interaction but requires that the malicious PDF be processed by the vulnerable pypdf version. The issue was resolved in version 6.6.2 by correcting the loop condition logic, and a pull request (#3610) contains the patch. Since pypdf is often embedded in various Python applications and services that handle PDF files, this vulnerability could be exploited by attackers to disrupt service availability by supplying crafted PDFs. No public exploits have been reported to date, but the medium CVSS score of 5.1 reflects the moderate impact and ease of exploitation given local access to the PDF file.

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 27 Jan 2026, 20:05 UTC

WeaknessesCWE-835

Technical details

References

Community reviews

Related threats