Service hang via catastrophic newline-regex backtracking
Published Aug 29, 2025 · Updated Aug 29, 2025
ReDoS in Turndown 7.2.0 through 7.2.1 allows remote attackers to hang applications by supplying crafted HTML for Markdown conversion. The blockquote and listItem replacement functions apply greedy trailing-newline regular expressions whose end anchors force excessive backtracking on long newline runs followed by a non-newline. Exploitation requires a consuming application to pass attacker-controlled HTML into an affected rule and exhausts CPU until the conversion process hangs.
Summary
What happened
ReDoS in Turndown 7.2.0 through 7.2.1 allows remote attackers to hang applications by supplying crafted HTML for Markdown conversion. The blockquote and listItem replacement functions apply greedy trailing-newline regular expressions whose end anchors force excessive backtracking on long newline runs followed by a non-newline. Exploitation requires a consuming application to pass attacker-controlled HTML into an affected rule and exhausts CPU until the conversion process hangs.
The record
- CVE
- CVE-2025-9670
- Published
- Aug 29, 2025
- Updated
- Aug 29, 2025
- Vendor
- mixmark-io
- Product
- Turndown
- Classifications
- CWE-1333, CWE-400, T1499
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 29, 2025CVE publishedPublication date reported by the CVE source.
- Aug 29, 2025Record 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=7.2.0
- Affected versionversion=7.2.1
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
- Turndown blockquote and listItem ReDoS proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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