exceljs: Unchecked Input for Loop Condition
CVE-2026-128343 is a high-severity unchecked input for loop condition vulnerability in exceljs, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected exceljs versions: 4.4.0 and earlier. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.68% chance of exploitation within 30 days, higher than 53% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of exceljs you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on github.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by CNA (vulncheck.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 8.7 | High | CNA (vulncheck.com) |
| CVSS 3.1 | 7.5 | High | CNA (vulncheck.com) |
Official description
exceljs through 4.4.0 contains a denial of service vulnerability that allows attackers to block the event loop by supplying unbounded row r attributes parsed in row-xform.js. Attackers can craft an XLSX file with a row numbered far beyond Excel's limit, making getSheetValues(), workbook writes and CSV export consume time proportional to that number.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Unchecked Input for Loop Condition
The product does not properly check inputs that are used for loop conditions, potentially leading to a denial of service or other consequences because of excessive looping.
How developers prevent this class of flaw
- Do not use user-controlled data for loop conditions.
More Unchecked Input for Loop Condition vulnerabilities (CWE-606)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
References
Other references
- github.com/exceljs/exceljs
- github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/worksheet.js#L571-L580
- github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/worksheet.js#L886-L893
- github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/row-xform.js#L73-L77
- vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-row-number
Other vulnerabilities in exceljs
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
Recent Unchecked Input for Loop Condition vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 7.1 High severity
- 8.2 High severity
- 8.8 High severity
- 8.6 High severity
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