Denial of service via quadratic byte concatenation
Published Aug 31, 2026 · Updated Sep 1, 2026
Inefficient algorithmic complexity in py-pdf pypdf before 6.15.0 allows attackers to cause long runtimes with a crafted PDF. The read_until_whitespace function reads one byte at a time and repeatedly concatenates immutable bytes, making a long non-whitespace run cost quadratic processing time. The vulnerable path is reached when an application processes attacker-controlled PDF data containing an extended byte sequence without whitespace, consuming CPU long enough to interrupt the hosting service.
Summary
What happened
Inefficient algorithmic complexity in py-pdf pypdf before 6.15.0 allows attackers to cause long runtimes with a crafted PDF. The read_until_whitespace function reads one byte at a time and repeatedly concatenates immutable bytes, making a long non-whitespace run cost quadratic processing time. The vulnerable path is reached when an application processes attacker-controlled PDF data containing an extended byte sequence without whitespace, consuming CPU long enough to interrupt the hosting service.
The record
- CVE
- CVE-2026-82398
- Published
- Aug 31, 2026
- Updated
- Sep 1, 2026
- Vendor
- py-pdf
- Product
- pypdf
- Classifications
- CWE-407, CWE-1046, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 31, 2026CVE publishedPublication date reported by the CVE source.
- Sep 1, 2026Record 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.
- Affected versionversion=< 6.15.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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