CVE-2026-28356Network attack vector

Request-handling interruption via ambiguous header regex

Published Mar 12, 2026 · Updated Mar 12, 2026

ReDoS in defnull multipart before 1.2.2 and version 1.3.0 allows remote attackers to interrupt request handling. The parse_options_header() function in multipart.py applies an ambiguously alternated regular expression to untrusted HTTP and part headers, causing exponential backtracking. A reachable WSGI or ASGI endpoint must parse the crafted header or multipart/form-data stream; each request can block a handling thread for several seconds.

CVSS severity7.5
High
EPSS probability0.72%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

ReDoS in defnull multipart before 1.2.2 and version 1.3.0 allows remote attackers to interrupt request handling. The parse_options_header() function in multipart.py applies an ambiguously alternated regular expression to untrusted HTTP and part headers, causing exponential backtracking. A reachable WSGI or ASGI endpoint must parse the crafted header or multipart/form-data stream; each request can block a handling thread for several seconds.

The record

CVE
CVE-2026-28356
Published
Mar 12, 2026
Updated
Mar 12, 2026
Vendor
defnull
Product
multipart
Classifications
CWE-1333, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 12, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 12, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.2.2
  2. Affected versionversion=>= 1.3.0, < 1.3.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

defnull · multipartversion=< 1.2.2; version=>= 1.3.0, < 1.3.1

Published CVSS scores

7.5GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1333Inefficient Regular Expression Complexity
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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