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CVE-2026-49851 is an algorithmic-complexity denial-of-service vulnerability in Mistune versions earlier than 3.3.0. Mistune's inline Markdown parser invokes parse_link_text for opening square brackets. For input containing many unmatched consecutive opening brackets, repeated regular-expression searches scan much of the remaining input and fail, after which parsing advances by only one character. The unrecorded failed search range causes repeated rescanning and approximately O(n²) processing. Version 3.3.0 replaces this behavior with linear-time closing-bracket mapping.
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No public exploit code observed for this vulnerability.
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Referenced vulnerability; no technical details are provided.
A denial-of-service vulnerability in the Mistune parser caused by quadratic-time parsing of unmatched sequential opening square brackets during link text parsing, leading to excessive CPU consumption.
A denial-of-service vulnerability in the Mistune Python Markdown parser caused by quadratic-time parsing in parse_link_text, allowing attacker-controlled Markdown input to trigger excessive CPU usage.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.