CVE-2023-36810Public exploit

Denial of service via quadratic reverse-line parsing

Published Jun 30, 2023 · Updated Feb 13, 2025

Algorithmic-complexity denial of service in py-pdf pypdf before 1.27.9 allows attackers to hang PDF-processing applications. PdfFileReader's readNextEndLine routine scans backward for the xref marker by prepending each byte to an immutable string, repeatedly copying the growing line and producing O(n²) work. Processing an attacker-supplied PDF with a missing end-of-file xref marker can monopolize one CPU core and block the hosting process without increasing memory use.

CVSS severity6.2
Medium
EPSS probability0.63%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Algorithmic-complexity denial of service in py-pdf pypdf before 1.27.9 allows attackers to hang PDF-processing applications. PdfFileReader's readNextEndLine routine scans backward for the xref marker by prepending each byte to an immutable string, repeatedly copying the growing line and producing O(n²) work. Processing an attacker-supplied PDF with a missing end-of-file xref marker can monopolize one CPU core and block the hosting process without increasing memory use.

The record

CVE
CVE-2023-36810
Published
Jun 30, 2023
Updated
Feb 13, 2025
Vendor
py-pdf
Product
pypdf
Classifications
CWE-407, T1499.004
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 30, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.27.9

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

py-pdf · pypdfversion=< 1.27.9

Published CVSS scores

6.2GitHubCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-407Inefficient Algorithmic Complexity
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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