CVE-2026-44660Public exploitNetwork attack vector

Memory exhaustion via unreleased serialized strings

Published May 27, 2026 · Updated May 27, 2026

Memory leak in UltraJSON before 5.12.1 allows remote attackers to exhaust application memory by forcing ujson.dump() write failures. The objToJSONFile() function returns after a file-like object’s write() raises an exception without decrementing the serialized Python string, leaking the entire payload allocation. Exposure requires application code to pass an attacker-influenced, failure-prone file-like object to ujson.dump(); repeated failures drive linear memory growth and interrupt the hosting service.

CVSS severity8.7
High
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory leak in UltraJSON before 5.12.1 allows remote attackers to exhaust application memory by forcing ujson.dump() write failures. The objToJSONFile() function returns after a file-like object’s write() raises an exception without decrementing the serialized Python string, leaking the entire payload allocation. Exposure requires application code to pass an attacker-influenced, failure-prone file-like object to ujson.dump(); repeated failures drive linear memory growth and interrupt the hosting service.

The record

CVE
CVE-2026-44660
Published
May 27, 2026
Updated
May 27, 2026
Vendor
UltraJSON
Product
UltraJSON
Classifications
CWE-401, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 27, 2026CVE publishedPublication date reported by the CVE source.
  2. May 27, 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=< 5.12.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

UltraJSON · UltraJSONversion=< 5.12.1

Published CVSS scores

8.7GitHubCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
7.5NIST NVDCVSS: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 exploitPublished

Weakness, pattern, technique

CWE-401Missing Release of Memory after Effective Lifetime
T1499.003Application Exhaustion Flood

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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