NVD / CVE Program· CNA GitHub_M

CVE-2023-26485: Quadratic complexity may lead to a denial of service in cmark-gfm

Noroxi assessment

Priority: Monitor (action score 30/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 1% (FIRST EPSS); higher than 63.6% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to CISA the attack is automatable: targets can be found by mass scanning.
Fixed version: github cmark-gfm 0.29.0.gfm.10.
Severity is disputed: the assigning authority (CNA) scores it 5.3, NVD 7.5.

Low priority for now. Upgrade to github cmark-gfm 0.29.0.gfm.10 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

cmark-gfm is GitHub's fork of cmark, a CommonMark parsing and rendering library and program in C. A polynomial time complexity issue in cmark-gfm may lead to unbounded resource exhaustion and subsequent denial of service. This CVE covers quadratic complexity issues when parsing text which leads with either large numbers of `_` characters. This issue has been addressed in version 0.29.0.gfm.10. Users are advised to upgrade. Users unable to upgrade should validate that their input comes from trusted sources. ### Impact A polynomial time complexity issue in cmark-gfm may lead to unbounded resource exhaustion and subsequent denial of service. ### Proof of concept ``` $ ~/cmark-gfm$ python3 -c 'pad = "_" * 100000; print(pad + "." + pad, end="")' | time ./build/src/cmark-gfm --to plaintext ``` Increasing the number 10000 in the above commands causes the running time to increase quadratically. ### Patches This vulnerability have been patched in 0.29.0.gfm.10. ### Note on cmark and cmark-gfm XXX: TBD [cmark-gfm](https://github.com/github/cmark-gfm) is a fork of [cmark](https://github.com/commonmark/cmark) that adds the GitHub Flavored Markdown extensions. The two codebases have diverged over time, but share a common core. These bugs affect both `cmark` and `cmark-gfm`. ### Credit We would like to thank @gravypod for reporting this vulnerability. ### References https://en.wikipedia.org/wiki/Time_complexity ### For more information If you have any questions or comments about this advisory: * Open an issue in [github/cmark-gfm](https://github.com/github/cmark-gfm)

HighCVSS 7.5 · v3.1—No exploit Fix available

Published: Mar 31, 2023
Updated: Jun 17, 2026
EPSS: 1.0% · 63th percentile
CWE: CWE-400

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 30 / 40 · 7.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 1.0%

CISA SSVC decision

Exploitation: proof of concept
Automatable: yes
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 7.5
CNA · GitHub_M: 5.3; 2.2 point gap

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Running WordPress? Scan your site free with WP Lens

Is your version affected? Check it

Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

We use this product, ask for help

Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
github	cmark-gfm	cpe:2.3:a:github:cmark-gfm

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

github cmark-gfmbefore 0.29.0.gfm.10

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

github cmark-gfm
- < 0.29.0.gfm.10affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	cmark-gfm	from 0	—
Debian:12	python-cmarkgfm	from 0	—
Debian:12	r-cran-commonmark	from 0	—
Debian:12	ruby-commonmarker	from 0	—
Debian:13	cmark-gfm	before 0.29.0.gfm.13-1	0.29.0.gfm.13-1
Debian:13	python-cmarkgfm	before 2024.11.20-1	2024.11.20-1
Debian:13	r-cran-commonmark	before 1.9.1-1	1.9.1-1
Debian:13	ruby-commonmarker	before 0.23.10-1	0.23.10-1

Same product

github: all records

Other highest-scoring records for the same primary product.

CVE-2022-24724Integer overflow in table parsing extension leads to heap memory corruption
40Plan
CVE-2024-22051CommonMarker Integer Overflow Vulnerability
39Monitor
CVE-2023-37463Quadratic complexity bugs may lead to a denial of service
30Monitor

Published before and after this one in the same product

← EarlierCVE-2023-22485Jan 23, 2023 · cmark-gfm out-of-bounds read in validate_protocol
21Monitor
← EarlierCVE-2023-22486Jan 26, 2023 · cmark-gfm Quadratic complexity bug in handle_close_bracket may lead to a denial of service
30Monitor
← EarlierCVE-2023-24824Mar 31, 2023 · Quadratic complexity may lead to a denial of service in cmark-gfm
30Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
github cmark-gfm	0.29.0.gfm.10 · description	Vendor (CNA)
debian:cmark-gfm	0.29.0.gfm.13-1 · Debian:13	Package registry (OSV)
debian:python-cmarkgfm	2024.11.20-1 · Debian:13	Package registry (OSV)
debian:r-cran-commonmark	1.9.1-1 · Debian:13	Package registry (OSV)
debian:ruby-commonmarker	0.23.10-1 · Debian:13	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

github/cmark-gfmcommit 07a66c9

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: none
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

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

nvd-primary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

Endpoint Denial of ServiceT1499

Change log

Fix✗ → ✓Sep 28, 2026, 10:49 PM UTC

For records you follow, these changes also arrive as notifications. →

References

github.com/github/cmark-gfm/commit/07a66c9bc341f902878e37d7da8647d6ef150987

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records