Security readout for executives and security teams
Plain-English summary
This is a browser-side self-XSS in @github/paste-markdown before 0.3.4. A user must be tricked into copying malicious clipboard content and pasting it into an application using the library. The business risk is targeted data exposure in that user's browser session, not server compromise. Vendor source says 0.3.4 fixes it.
Executive priority
Treat as a targeted browser-session data exposure risk. Prioritize remediation where the vulnerable library appears in authenticated, sensitive, or administrative web workflows. Broad emergency response is not supported by the provided evidence.
Technical view
When pasted clipboard data includes table markup, vulnerable versions create a div and assign clipboard content to innerHTML without sanitization. That can execute JavaScript in the victim's browser after paste. CVSS 3.1 is 6.5, with network attack vector, low complexity, no privileges, required user interaction, and high confidentiality impact.
Likely exposure
Exposure is limited to web pages or products that include @github/paste-markdown versions before 0.3.4 and accept user paste actions. The source bundle does not identify other affected products or downstream applications.
Exploitation context
Sources describe social engineering: users copy text from a malicious website and paste it into an affected page. The source bundle marks KEV false and provides no evidence of active exploitation in the wild.
Researcher notes
The advisory attributes the issue to unsanitized innerHTML handling during paste processing. Validation should focus on dependency version, reachable paste surfaces, and whether sensitive session data is accessible in affected browser contexts. Do not assume impact beyond the library without product-specific evidence.
Mitigation direction
- Upgrade @github/paste-markdown to version 0.3.4 or later.
- Inventory frontend dependencies for @github/paste-markdown below 0.3.4.
- Check vendor guidance and release notes before deploying dependency updates.
- Review applications that transform pasted clipboard content into HTML.
Validation and detection
- Inspect package lockfiles for @github/paste-markdown versions below 0.3.4.
- Confirm affected pages use the upgraded library in built frontend assets.
- Run existing paste-handling regression tests after dependency update.
- Verify dependency scanning flags are cleared for CVE-2021-37700.
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
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-79: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. 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-2021-37700 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
- Medium
- CVSS
- 6.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
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:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N2.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.5MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/github/paste-markdown/security/advisories/GHSA-gpfj-4j6g-c4w9CVE reference · x_refsource_CONFIRM
- https://github.com/github/paste-markdown/commit/32b7ea3f29ae8f256f9d19768387be42678ddf30CVE reference · x_refsource_MISC
- https://github.com/github/paste-markdown/releases/tag/v0.3.4CVE reference · x_refsource_MISC
- https://www.npmjs.com/package/%40github/paste-markdownCVE reference · x_refsource_MISC
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.
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.