Service interruption via quadratic XML indentation amplification
Published Sep 7, 2026 · Updated Sep 10, 2026
Asymmetric resource consumption in The PHP League CommonMark 2.0.0 through 2.8.3 allows remote attackers to exhaust server resources. XmlRenderer emits indentation proportional to every nested tag's full depth, so small attacker-controlled Markdown or AST inputs produce quadratically large XML output and memory use. Exposure requires an application to route untrusted content through the opt-in XML renderer; the result is memory and output-size amplification, not data disclosure or modification.
Summary
What happened
Asymmetric resource consumption in The PHP League CommonMark 2.0.0 through 2.8.3 allows remote attackers to exhaust server resources. XmlRenderer emits indentation proportional to every nested tag's full depth, so small attacker-controlled Markdown or AST inputs produce quadratically large XML output and memory use. Exposure requires an application to route untrusted content through the opt-in XML renderer; the result is memory and output-size amplification, not data disclosure or modification.
The record
- CVE
- CVE-2026-86432
- Published
- Sep 7, 2026
- Updated
- Sep 10, 2026
- Vendor
- The PHP League
- Product
- CommonMark
- Classifications
- CWE-405, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 7, 2026CVE publishedPublication date reported by the CVE source.
- Sep 10, 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=2.0.0 <2.8.4
What conditions does exploitation require?
What is affected?
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
- Nested blockquote XML amplification triggerproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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