Service degradation via quadratic ASCIIHex decoding
Published Mar 6, 2026 · Updated Mar 6, 2026
Inefficient decoding in py-pdf pypdf before 6.7.5 allows remote attackers to cause long runtimes via crafted PDF streams. ASCIIHexDecode.decode repeatedly concatenates immutable byte strings while parsing input one character at a time, causing quadratic copying as the stream grows. Exploitation requires an application to access an attacker-controlled stream using the /ASCIIHexDecode filter; the reported consequence is prolonged processing rather than a crash.
Summary
What happened
Inefficient decoding in py-pdf pypdf before 6.7.5 allows remote attackers to cause long runtimes via crafted PDF streams. ASCIIHexDecode.decode repeatedly concatenates immutable byte strings while parsing input one character at a time, causing quadratic copying as the stream grows. Exploitation requires an application to access an attacker-controlled stream using the /ASCIIHexDecode filter; the reported consequence is prolonged processing rather than a crash.
The record
- CVE
- CVE-2026-28804
- Published
- Mar 6, 2026
- Updated
- Mar 6, 2026
- Vendor
- py-pdf
- Product
- pypdf
- Classifications
- CWE-407, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 6, 2026CVE publishedPublication date reported by the CVE source.
- Mar 6, 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=< 6.7.5
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
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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