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CVE-2026-55206— py7zr: O(n^2) algorithmic complexity DoS in PackInfo._read()

Quick assessment

Affected
miurahr py7zr
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Hiroshi Miura py7zr是日本Hiroshi Miura个人开发者的一个7z文件压缩解压的Python库。 Hiroshi Miura py7zr 1.1.3之前版本存在资源管理错误漏洞，该漏洞源于archiveinfo.py中的PackInfo._read()使用了O(n^2)累积求和模式处理攻击者控制的消息流解析值，可能导致在提取前造成CPU过度消耗。

AI Predicted 7.5 Difficulty: Easy EPSS 0.32% · P23

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 1

VendorProduct Version RangeStatus
miurahr py7zr < 1.1.3 affected
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I. Basic Information for CVE-2026-55206

Vulnerability Information
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Vulnerability Title
py7zr: O(n^2) algorithmic complexity DoS in PackInfo._read()
Source: CVE Program / CVE List V5
Vulnerability Description
py7zr is a Python-based library and utility to support 7zip archive compression, decompression, encryption and decryption. Prior to 1.1.3, PackInfo._read() in archiveinfo.py used an O(n^2) cumulative sum pattern for attacker-controlled numstreams values parsed from archive headers, allowing a crafted .7z archive to cause excessive CPU consumption during SevenZipFile.init() before extraction. This issue is fixed in version 1.1.3.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
算法复杂性
Source: CVE Program / CVE List V5
Vulnerability Title
Hiroshi Miura py7zr 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Hiroshi Miura py7zr是日本Hiroshi Miura个人开发者的一个7z文件压缩解压的Python库。 Hiroshi Miura py7zr 1.1.3之前版本存在资源管理错误漏洞，该漏洞源于archiveinfo.py中的PackInfo._read()使用了O(n^2)累积求和模式处理攻击者控制的消息流解析值，可能导致在提取前造成CPU过度消耗。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
miurahr py7zr < 1.1.3 -

II. Public POCs for CVE-2026-55206

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III. Intelligence Information for CVE-2026-55206

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Patches & Fixes for CVE-2026-55206 (2)

Vendor Advisories for CVE-2026-55206 (1)

IV. Related Vulnerabilities

Same product: py7zr
Same vendor: miurahr
Same weakness: CWE-407

V. Comments for CVE-2026-55206

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