Marked: OOM Denial of Service via Infinite Recursion in marked Tokenizer

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Marked is a markdown parser and compiler. From 18.0.0 to 18.0.1, a critical Denial of Service (DoS) vulnerability exists in marked. By providing a specific 3-byte input sequence a tab, a vertical tab, and a newline (\x09\x0b\n)—an unauthenticated attacker can trigger an infinite recursion loop during parsing. This leads to unbounded memory allocation, causing the host Node.js application to crash via Memory Exhaustion (OOM). This vulnerability is fixed in 18.0.2.

Source published

24 Apr 2026 17:26:27 UTC

Source modified

24 Apr 2026 19:08:41 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Marked is a markdown parser and compiler. From 18.0.0 to 18.0.1, a critical Denial of Service (DoS) vulnerability exists in marked. By providing a specific 3-byte input sequence a tab, a vertical tab, and a newline (\x09\x0b\n)—an unauthenticated attacker can trigger an infinite recursion loop during parsing. This leads to unbounded memory allocation, causing the host Node.js application to crash via Memory Exhaustion (OOM). This vulnerability is fixed in 18.0.2.

Source published

Apr 24, 2026, 5:26:27 PM (timezone not stated)

Source modified

Apr 24, 2026, 7:08:41 PM (timezone not stated)

Observed here

28 Oct 2026 05:10:49 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Marked is a markdown parser and compiler. From 18.0.0 to 18.0.1, a critical Denial of Service (DoS) vulnerability exists in marked. By providing a specific 3-byte input sequence a tab, a vertical tab, and a newline (\x09\x0b\n)—an unauthenticated attacker can trigger an infinite recursion loop during parsing. This leads to unbounded memory allocation, causing the host Node.js application to crash via Memory Exhaustion (OOM). This vulnerability is fixed in 18.0.2.

Source published

24 Apr 2026 18:16:29 UTC

Source modified

26 Oct 2026 21:10:00 UTC

Observed here

27 Oct 2026 10:10:19 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Primary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

### Summary A critical Denial of Service (DoS) vulnerability exists in `[email protected]`. By providing a specific 3-byte input sequence a tab, a vertical tab, and a newline (`\x09\x0b\n`)—an unauthenticated attacker can trigger an infinite recursion loop during parsing. This leads to unbounded memory allocation, causing the host Node.js application to crash via Memory Exhaustion (OOM). ### Details The vulnerability originates in how `marked`'s block tokenizer handles unexpected whitespace characters. 1. **Tab Character (`\x09`) Consumption**: The `space()` tokenizer matches standard whitespace using the regex `/^(?:[ \t]*(?:\n|$))+/`. When parsing the malicious payload (`\x09\x0b\n`), this rule successfully consumes the initial tab character (`\x09`). 2. **Vertical Tab (`\x0b`) Bypass**: The remaining input is now `\x0b\n`. The newline block rule explicitly looks for spaces or standard tabs (`[ \t]`) followed by a newline. Because the vertical tab is a legacy ASCII character not accounted for in this rule, it fails to match. 3. **Fallback to Text Tokenizer**: None of the standard block tokenizers (blockquote, code, heading, etc.) match `\x0b\n`. As a result, the parser falls through to the `text` tokenizer (`/^[^\n]+/`), which matches any character except a newline. 4. **Infinite Recursion**: Inside `blockTokens()`, the `text` tokenizer creates a text token and subsequently calls `inlineTokens()` on the exact same content. Inside `inlineTokens()`, the text rule again matches `\x0b\n` and recursively calls `inlineTokens()`. This creates an inescapable cycle: `blockTokens() → text token → inlineTokens() → text rule matches → inlineTokens() → ...` With each recursive call allocating new token objects and concatenating strings, memory grows indefinitely until the Node.js heap limit is reached. **Vulnerable Code in `lib/marked.esm.js` (Lexer class, `blockTokens()`):** ```javascript // The text tokenizer triggers infinite recursion if(r=this.tokenizer.text(e)) { e=e.substring(r.raw.length); let s=t.at(-1); s?.type==="text"?(s.raw+=(s.raw.endsWith("\n")?"":"\n")+r.raw, s.text+="\n"+r.text, this.inlineQueue.pop(), this.inlineQueue.at(-1).src=s.text):t.push(r); // ↑ This calls inlineTokens() internally via the text tokenizer, causing the OOM loop continue; } ``` ### PoC This vulnerability can be reproduced using any standard Node.js environment with `[email protected]` installed. 1. Create a file named `poc.js` with the following content: ```javascript const marked = require('marked'); // The vulnerable 3-byte pattern: tab + vertical tab + newline const vulnerableInput = '\x09\x0b\n'; console.log('Attempting to parse malicious payload...'); try { marked.parse(vulnerableInput); } catch(e) { console.log('Error:', e.message); } ``` 2. Run the script: `node poc.js` 3. **Result:** The process will hang briefly as memory spikes, ultimately crashing with: `FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory`. ### Impact This is a High-Severity Denial of Service (DoS) vulnerability via Memory Exhaustion. **Impacted Parties:** Any application, API, chatbot, or documentation system using `[email protected]` (and potentially earlier versions) to parse untrusted user input is vulnerable. Because the payload requires zero authentication and only 3 bytes of data, it requires virtually no resources from the attacker to remotely crash the service and achieve a total loss of availability for the targeted application.

Source published

29 Apr 2026 22:12:20 UTC

Source modified

5 May 2026 16:11:33 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Publisher rating · HIGH