Security readout for executives and security teams
Plain-English summary
HTML2Markdown can be made to spend excessive CPU time while converting specially crafted HTML to Markdown. The main business risk is denial of service in applications that process untrusted HTML through this library. The sources state no known patches were available at publication, so exposure management may require replacement or containment.
Executive priority
Treat as high priority for internet-facing services that convert user-supplied HTML. For internal-only or unused dependency exposure, prioritize inventory confirmation first, then remove, replace, or contain affected use.
Technical view
CVE-2020-26307 covers ReDoS in kates/html2markdown, a JavaScript HTML-to-Markdown converter. All available versions were reported affected by vulnerable regular expressions. CVSS 4.0 is 8.7 with network, low-complexity, unauthenticated attack conditions and high vulnerable-system availability impact.
Likely exposure
Exposure is likely only where kates/html2markdown is present and receives attacker-controlled or externally supplied HTML. Public web forms, APIs, importers, email processors, and background conversion jobs would be higher concern if they call this library.
Exploitation context
The source bundle shows no KEV listing and provides no evidence of active exploitation. Public advisory details confirm the vulnerability class and affected project, but they do not establish real-world exploitation.
Researcher notes
The CVE record lists CWE-1333 and high availability impact. Evidence is limited to the CVE data, GitHub Security Lab advisory, and GitHub issue. No source in the bundle identifies a fixed release or active exploitation.
Mitigation direction
- Check current vendor or maintainer guidance before assuming a patch exists.
- Replace the package if no maintained fixed version is available.
- Avoid passing untrusted HTML into this converter where possible.
- Apply input size limits and request timeouts around conversion paths.
- Rate-limit endpoints that trigger HTML-to-Markdown conversion.
Validation and detection
- Search dependency manifests, lockfiles, and SBOMs for kates/html2markdown.
- Map all application paths that call HTML-to-Markdown conversion.
- Confirm whether conversion input can be supplied by external users.
- Review production metrics for slow or hanging conversion operations.
- Track remediation decisions where no vendor patch is confirmed.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
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CWE-1333: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2020-26307 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.7 (4.0)
- Known Exploited
- No
- Published
Vector: 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/U:Green
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
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/U:Green——Primary CVE scoreVulnerability scoring details
Base CVSS 4.0 score
8.7HighVector: 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/U:Green
Source materials
- CVE List V5 sourceCVE List V5
- https://securitylab.github.com/advisories/GHSL-2020-301-redos-HTML2Markdown/CVE reference
- https://github.com/kates/html2markdown/issues/13CVE reference
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Inefficient Regular Expression Complexity
Inefficient Regular Expression Complexity represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.