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CVE-2026-44660 high CVSS 7.5

Vulnerability in ujson (CVE-2026-44660)

Summary

Vulnerability in ujson (CVE-2026-44660). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 5.12.1 or later.

Original description

The description as published by the source.

Summary

When ujson.dump() writes to a file-like object and the write operation raises an exception, the serialized JSON string object is not decremented, leaking memory. Each failed write operation leaks the full size of the serialized payload.

Code that uses ujson.dumps() rather than ujson.dump() or only JSON load/decode methods is unaffected.

Details

Vulnerability Location:

  • src/ujson/python/objToJSON.c:913 - objToJSONFile() function start
  • src/ujson/python/objToJSON.c:931 - Error return on write failure
  • src/ujson/python/objToJSON.c:942 - Early return without cleanup

Root Cause:

The objToJSONFile() function allocates a Python string object via ujson_dumps_internal(), calls the file's write() method, and returns early if write() raises an exception—but never calls Py_DECREF(string) on the early exit path.

PoC

import gc, tracemalloc, ujson

class BadFile:
    def write(self, s):
        raise RuntimeError("boom")

obj = {"x": "A" * 200000}

def run():
    try:
        ujson.dump(obj, BadFile())
    except RuntimeError:
        pass

run()
tracemalloc.start()
gc.collect()
base = tracemalloc.get_traced_memory()[0]

for i in range(5):
    run()
    gc.collect()
    cur = tracemalloc.get_traced_memory()[0]
    print(i, cur - base)

Impact

Any application that serializes data through ujson.dump() to an attacker-influenced file-like object that can fail can be driven into linear memory growth. An attacker…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-44660 has been found in ujson.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade ujson to 5.12.1 or later.
If unsure, ask your IT team or search "ujson CVE-2026-44660" on the vendor's site.

CVE-2026-44660 (ujson) — CWE-401 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 5.12.1 — apply immediately
Workaround: Replacing ujson.dump(obj, file) with file.write(ujson.dumps(obj)) is equivalent (contrary to popular misconception, there are no streaming benefits to using ujson.dump()) and will avoid the memory leak.
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-401) exists in ujson.

📍 Affected scope

Check the vendor advisory for the affected versions of ujson.

🔥 Severity

Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 5.12.1.

🛡️ Workaround

Workaround: Replacing ujson.dump(obj, file) with file.write(ujson.dumps(obj)) is equivalent (contrary to popular misconception, there are no streaming benefits to using ujson.dump()) and will avoid the memory leak.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'ujson' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'ujson' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で ujson を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply temporary workaround mitigate 
    Replacing `ujson.dump(obj, file)` with `file.write(ujson.dumps(obj))` is equivalent (contrary to popular misconception, there are no streaming benefits to using `ujson.dump()`) and will avoid the memory leak.

    パッチが適用されるまでの応急処置として、Replacing ujson.dump(obj, file) with file.write(ujson.dumps(obj)) is equivalent (contrary to popular misconception, there are no streaming benefits to using ujson.dump()) and will avoid the memory leak. を実施。回避策の副作用 (機能低下) を確認した上で。

  3. 3
    Apply patch patch 
    Upgrade ujson to 5.12.1

    ステージング環境で 5.12.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  4. 4
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

pip ujson
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.12.1"}]}]
PyPI ujson
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.12.1"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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