VulnerabilityPublished 6 Mar 2026

CVE-2026-28804: py-pdf pypdf · Inefficient Algorithmic Complexity

Affects py-pdf pypdfSource CVE Database V5

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Not known to be exploited · CVSS 6.9 Medium : upgrade to 6.7.5 when convenient.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 4.0 base score

6.9Medium

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

EPSS: 0.4% chance of exploitation in 30 days – higher than 35% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 6.7.5

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

Attack Vector: Network
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: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
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 6 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 29 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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), 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 6.7.5.

Affected software

Product	Affected	Fixed in
py-pdfpypdf	Affected <6.7.5	Fixed in 6.7.5
PyPIpypdf`pkg:pypi/pypdf`Other threats	Affected <6.7.5	Fixed in 6.7.5

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

AI-suggested

To mitigate CVE-2026-28804, organizations should immediately upgrade all instances of the pypdf library to version 6.7.5 or later, where the vulnerability is patched. For environments where immediate upgrade is not feasible, implement input validation and filtering to block or sanitize PDF files containing /ASCIIHexDecode streams from untrusted sources. Employ rate limiting and resource usage monitoring on PDF processing services to detect and mitigate abnormal processing times indicative of exploitation attempts. Consider sandboxing or isolating PDF processing components to contain potential denial of service impacts. Additionally, maintain updated threat intelligence to monitor for any emerging exploits targeting this vulnerability. Regularly audit and update third-party dependencies like pypdf to ensure timely application of security patches. Finally, educate developers and system administrators about the risks of algorithmic complexity vulnerabilities and the importance of secure PDF handling.

Description

### Impact An attacker who uses this vulnerability can craft a PDF which leads to long runtimes. This requires accessing a stream which uses the `/ASCIIHexDecode` filter. ### Patches This has been fixed in [pypdf==6.7.5](https://github.com/py-pdf/pypdf/releases/tag/6.7.5). ### Workarounds If you cannot upgrade yet, consider applying the changes from PR [#3666](https://github.com/py-pdf/pypdf/pull/3666).

Impact

The primary impact of CVE-2026-28804 is a denial of service condition caused by resource exhaustion due to inefficient processing of crafted PDF files. Organizations using vulnerable versions of pypdf in automated PDF processing pipelines, document management systems, or web services that accept PDF uploads are at risk. Exploitation could lead to application slowdowns, crashes, or unavailability, disrupting business operations and potentially causing service outages. Since the vulnerability does not affect confidentiality or integrity, data breaches or unauthorized data modification are unlikely. However, the availability impact can be significant for high-volume or critical PDF processing environments. Attackers could leverage this vulnerability to perform targeted DoS attacks against organizations that rely on pypdf, especially if exposed to untrusted PDF inputs. The lack of authentication or user interaction requirements increases the risk of exploitation. While no known exploits exist currently, the medium severity and ease of exploitation warrant prompt remediation to prevent future attacks.

Summary

CVE-2026-28804 is an algorithmic complexity vulnerability classified under CWE-407 affecting the py-pdf pypdf library versions prior to 6.7.5. The vulnerability arises when the library processes PDF streams filtered with /ASCIIHexDecode. An attacker can craft a malicious PDF file that causes the library to enter a state of inefficient processing, leading to significantly prolonged runtimes. This can result in resource exhaustion, effectively causing a denial of service (DoS) condition in applications that parse or manipulate PDFs using the vulnerable pypdf versions. The vulnerability does not require any privileges, authentication, or user interaction, making it remotely exploitable by simply providing the malicious PDF input. The root cause is the inefficient handling of the ASCIIHexDecode filter stream, which can be exploited to trigger excessive CPU consumption. The issue was addressed and patched in pypdf version 6.7.5, which optimizes the decoding process to prevent such runtime degradation. The CVSS 4.0 vector indicates network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), and low impact on availability (VA:L), with no impact on confidentiality or integrity. No known exploits have been reported in the wild as of the publication date. This vulnerability primarily affects any software or services that rely on pypdf for PDF processing and have not updated to the fixed version.

CWE-407Inefficient Algorithmic Complexity (opens in a new tab)
Class weaknessLikelihood of exploit: Low
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 6 Mar 2026, 07:15 UTC

WeaknessesCWE-407

Technical details

References

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