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multiparty vulnerable to ReDoS via filename parsing

High severity GitHub Reviewed Published May 12, 2026 in pillarjs/multiparty

Package

npm multiparty (npm)

Affected versions

<= 4.2.3

Patched versions

4.3.0

Description

Impact

multiparty@4.2.3 and lower versions are vulnerable to denial of service via regular expression backtracking in the Content-Disposition filename parameter parser. A multipart upload with a long header value containing !filename="1 repeated can cause regex matching to take seconds, blocking the event loop. Any service accepting multipart uploads via multiparty is affected.

Patches

Users should upgrade to multiparty@4.3.0 or higher.

Workarounds

None. Limiting upload sizes at the proxy/gateway layer reduces but does not eliminate the attack surface, since a small ~8 KB header is sufficient to trigger the vulnerable backtracking.

Resources

References

@UlisesGascon UlisesGascon published to pillarjs/multiparty May 12, 2026
Published by the National Vulnerability Database May 12, 2026
Published to the GitHub Advisory Database May 18, 2026
Reviewed May 18, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

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

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(18th percentile)

Weaknesses

Inefficient Regular Expression Complexity

The product uses a regular expression with an inefficient, possibly exponential worst-case computational complexity that consumes excessive CPU cycles. Learn more on MITRE.

CVE ID

CVE-2026-8159

GHSA ID

GHSA-65x3-rw7q-gx94

Source code

Credits

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