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CVE Record

CVE-2026-32874: UltraJSON has a Memory Leak parsing large integers allows DoS

UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Versions 5.4.0 through 5.11.0 contain an accumulating memory leak in JSON parsing large (outside of the range [-2^63, 2^64 - 1]) integers. The leaked memory is a copy of the string form of the integer plus an additional NULL byte. The leak occurs irrespective of whether the integer parses successfully or is rejected due to having more than sys.get_int_max_str_digits() digits, meaning that any sized leak per malicious JSON can be achieved provided that there is no limit on the overall size of the payload. Any service that calls ujson.load()/ujson.loads()/ujson.decode() on untrusted inputs is affected and vulnerable to denial of service attacks. This issue has been fixed in version 5.12.0.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

UltraJSON versions 5.4.0 through 5.11.0 can leak memory when parsing very large integers in JSON. Internet-facing services that parse untrusted JSON with ujson can be forced to consume memory until availability is affected. The vendor fixed the issue in 5.12.0.

Executive priority

Prioritize remediation for public or partner-facing Python APIs using UltraJSON. The issue is straightforward denial of service, not data theft, but affected services can lose availability under malicious input.

Technical view

The bug is an accumulating memory leak in ujson.load(), ujson.loads(), and ujson.decode() when parsing integers outside [-2^63, 2^64 - 1]. The leak includes the integer string plus a NULL byte and occurs even when Python rejects oversized digit counts. Impact is availability only: CVSS 7.5, CWE-401/CWE-772.

Likely exposure

Exposure is most likely in Python services using ultrajson/ujson 5.4.0 through 5.11.0 on untrusted JSON, especially public APIs without strict body-size limits.

Exploitation context

The source bundle does not show CISA KEV listing or confirmed active exploitation. Abuse would depend on reaching a parser path with large attacker-controlled JSON input and sufficient request size allowance.

Researcher notes

Key evidence comes from the GitHub advisory, CVE record, release note, and fixing commit. The bundle names no exploit in the wild. Scope should remain limited to ultrajson 5.4.0 through 5.11.0 and untrusted JSON parsing paths.

Mitigation direction

  • Upgrade ultrajson to version 5.12.0 or later.
  • Apply vendor or distribution guidance for packaged ultrajson builds.
  • Limit maximum JSON request body size at application and edge layers.
  • Avoid parsing untrusted JSON with affected ujson versions until upgraded.
  • Monitor memory growth and worker restarts on JSON-heavy endpoints.

Validation and detection

  • Inventory Python dependencies for ultrajson or ujson versions 5.4.0 through 5.11.0.
  • Trace externally reachable code paths calling ujson.load, ujson.loads, or ujson.decode.
  • Confirm request size limits exist before JSON parsing occurs.
  • Verify deployed artifacts use ultrajson 5.12.0 or later.
  • Review Red Hat package status where distribution packages are used.
Prepared
Confidence
high
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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 · low confidence lookup

CWE-401: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. 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.

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cwe · low confidence lookup

CWE-772: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. 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.

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cve · low confidence lookup

CVE-2026-32874 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Official CVE source material

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.

2CVSS vectors
5Timeline events
2ADP providers
7Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: partial

CVSS vector scores

2 official scores

We 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.

ScoreVersionSeverityVectorExploitImpactSource
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6GitHub_M
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-32874Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPUltraJSON: UltraJSON: Denial of Service due to memory leak when parsing large integers
other:Red Hat severity ratingcvssV3_1
  • 2026-03-20T03:03:11.302Z: Reported to Red Hat.
  • 2026-03-20T01:31:30.207Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
ultrajsonultrajson>= 5.4.0, < 5.12.0Listed
Weakness

CWE details

CWE-401CWE-772

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.