CVE-2026-68498

Executive Summary

CVE-2026-68498 is a denial-of-service vulnerability in a JSON parser implementation that exposes the StreamReadConstraints.maxNameLength configuration (default 50,000 characters). Because the character-input parsing path (ReaderBasedJsonParser) fails to enforce the name-length bound while a property name is being accumulated, an attacker who can have a single oversized JSON Object property name parsed can force allocation on the order of 100,000,000 characters (approximately 200 MB per request) before any StreamConstraintsException is thrown. Any application that parses untrusted JSON from network sources using the affected character-input parser path is potentially affected; impact is limited to availability (CVSS 7.5, A:H), with no confidentiality or integrity impact observed.

Technical Analysis

The vulnerability is a resource-consumption flaw (CWE-400, Uncontrolled Resource Consumption) in the character-input parsing path of the affected JSON library. The StreamReadConstraints API defines two independent bounds: maxStringLength (default 100,000,000 characters) for ordinary string values, and maxNameLength (default 50,000) specifically intended to bound memory consumed by a single JSON Object property name during parsing.

For parsers built over character input — Reader, String, or char[] sources, all served by ReaderBasedJsonParser — the name-length bound is not applied while the name is being accumulated. The code path instead re-uses the string-value length check, which is roughly 2,000x larger by default.

At the code level: in the character-input slow path, ReaderBasedJsonParser._parseName2() accumulates the name into the TextBuffer and, when a segment fills, calls TextBuffer.finishCurrentSegment(), which validates only maxStringLength. The correct check, StreamReadConstraints.validateNameLength(int), is only reached afterwards in CharsToNameCanonicalizer.findSymbol(), once the entire name has been scanned to its closing quote. By that point the full name — up to maxStringLength characters — has already been buffered in memory.

The result is that the parser allocates up to roughly 100,000,000 characters (about 200 MB, with segment bookkeeping pushing real peak usage higher) before throwing StreamConstraintsException, instead of the approximately 50,000-character (about 100 KB) bound the API contract promises. The amplification factor between promised and actual allocation is therefore approximately 4,000x in character count.

The attack surface is any service endpoint that deserializes JSON from untrusted network input using a parser constructed over character-based sources (Reader, String, or char[]). This is a broad class that includes typical web-framework JSON body parsing, message-queue consumers, and inter-service RPC handlers. The flaw is triggered purely by input shape and requires no authentication.

Exploitation Scenarios

No public PoC or exploit code is available; the attack chain below is inferred from the vulnerability class and the mechanism described in the NVD entry.

1. Reconnaissance / target identification. An attacker identifies an application endpoint or message channel that accepts JSON documents from untrusted sources and that internally uses the character-input parser path (ReaderBasedJsonParser). This can be inferred from the application's technology stack and observed behavior (e.g., how malformed JSON is handled and whether constraint exceptions are surfaced).

2. Triggering the flaw class. The attacker submits a JSON document containing a single Object property name that is far longer than the configured maxNameLength but within maxStringLength. Because the input path is character-based, name accumulation in TextBuffer occurs without the validateNameLength check until the closing quote is reached. The constraint is therefore enforced only after the oversized name has been fully buffered.

3. Payload / execution at class level. The payload is a syntactically valid (or nearly valid) JSON object with an extremely long property name string. No special characters or injection are required — the vulnerability is triggered purely by string length. The attacker controls how close the name length approaches maxStringLength (default 100,000,000 characters), and therefore controls the memory allocation magnitude per request.

4. Post-exploitation impact. Each malicious request forces allocation on the order of hundreds of megabytes. Repeating this across concurrent requests — as the NVD description explicitly notes — multiplies memory pressure. The observable outcome is heap exhaustion, excessive garbage-collection churn, elevated latency, and ultimately process-level OutOfMemoryError or unresponsiveness. Impact is availability-only; the attacker gains no code execution, data access, or persistence.

Impact Assessment

CVSS 3.1 base score is 7.5 (High) with vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

• Attack Vector (Network): exploitable remotely over any network channel delivering JSON to the parser.
• Attack Complexity (Low): the flaw is triggered by input length alone; no race conditions or special timing required.
• Privileges Required (None) / User Interaction (None): no authentication required; no victim interaction needed.
• Confidentiality / Integrity (None): no data disclosure or modification.
• Availability (High): repeated or concurrent oversized names can exhaust heap and render the service unavailable.

Business impact: For internet-facing APIs, message brokers, or microservice endpoints, the practical blast radius is every instance that deserializes untrusted JSON via the character-input path. Because the default maxNameLength protection is effectively bypassed, operators who believe they are protected by a 50 KB name bound are in fact exposed to allocations up to ~200 MB per request. Peak memory usage is further inflated by TextBuffer segment bookkeeping. Services with constrained heap (containers, serverless runtimes) are at greatest risk of full denial of service. No known threat actor campaigns, CISA KEV listing, or exploit-in-the-wild evidence exists at this time.

Detection Guidance

Sigma Rule

title: Oversized JSON Property Name (CVE-2026-68498 DoS Attempt)
id: 7c2f9a41-8b6e-4d1a-9f0c-2e5b6d7a8c19
status: experimental
description: Detects JSON request bodies or log events containing an abnormally long property name indicative of CVE-2026-68498 exploitation.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-68498
author: valtersit.com
date: 2026/01/01
logsource:
  category: webserver
detection:
  selection_content:
    c-uri|contains: '":'
  selection_length:
    cs-uri-query|re: '\{[^}]{50000,}'
  condition: selection_length
fields:
  - c-ip
  - cs-method
  - c-uri
falsepositives:
  - Legitimate bulk data upload of large JSON documents (rare)
level: medium
tags:
  - attack.t1190
  - cwe.400

YARA Rule

rule CVE_2026_68498_Oversized_Json_Property_Name
{
    meta:
        description = "Detects JSON payloads with a property name exceeding the maxNameLength default of 50000 chars (CVE-2026-68498)"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-68498"
        cve = "CVE-2026-68498"
        date = "2026-01-01"

    strings:
        $obj_start = "{"
        $key_open  = "\""

    condition:
        filesize > 50KB and
        $obj_start at 0 and
        for any i in (1..#obj_start) : ( $key_open in (0..60000) ) and
        not defined pe.entry_point
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-68498 Potential JSON Property Name DoS Attempt (oversized key)"; flow:to_server,established; http.method; content:"POST"; http.request_body; content:"{"; content:"\""; pcre:"/\{[^\}]{50000,}/s"; threshold: type both, track by_src, count 5, seconds 60; classtype:attempted-dos; sid:202668498; rev:1;)

Elastic Detection

sequence by source.ip with maxspan=60s
  [network where destination.port in (80, 443, 8080, 8443) and
   http.request.method == "POST" and
   http.request.body.bytes >= 1000000]
  [network where http.request.method == "POST" and
   http.request.body.bytes >= 1000000]

Splunk SPL Query

index=web OR index=proxy sourcetype=access_combined
| eval body_len=coalesce(content_length, bytes, 0)
| where (method=="POST" AND body_len > 1000000)
| stats count AS oversized_requests,
        sum(body_len) AS total_bytes,
        values(uri_path) AS targets
        by src_ip
| where oversized_requests >= 5
| sort - oversized_requests

Wazuh OSSEC Rule

<group name="web,attack,cve-2026-68498,">
  <rule id="2026684" level="8">
    <if_sid>31103,31533</if_sid>
    <match>content-length</match>
    <regex>Content-Length: [1-9][0-9]{6,}</regex>
    <description>CVE-2026-68498: Oversized JSON request body may trigger property-name memory exhaustion</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>cwe_400,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate mitigations

• Enforce body-size limits at the edge (reverse proxy / API gateway) below the maxNameLength and maxStringLength defaults — e.g., cap request bodies well under 50 KB where business logic permits — so oversized property names are rejected before reaching the parser.
• Prefer the byte-input parser path (e.g., ByteSourceJsonBootstrapper/UTF-8 byte-based parsing) for untrusted input where the code path applies, since the flaw is specific to the character-input path (Reader, String, char[]).
• Apply per-source rate limiting and concurrency caps on JSON-accepting endpoints to blunt amplification from repeated concurrent requests.
• Monitor JVM heap and GC telemetry; alert on abnormal allocation spikes correlated with large inbound request bodies.
• Reduce container/JVM heap headroom only to limits that are safe against a single malicious request once edge limits are in place.

2. Patch / upgrade steps

• No vendor advisory or fixed version is currently published. Track the upstream library's release notes for a fix that moves the validateNameLength check into TextBuffer.finishCurrentSegment() or earlier in _parseName2() accumulation.
• When a patched release becomes available, upgrade affected services and verify that oversized property names now raise StreamConstraintsException before buffering — test with a name length between 50,001 and the configured maxStringLength.

3. Long-term hardening

• Treat all deserialized input as adversarial; enforce input-size and schema limits before parse.
• Fuzz JSON-facing endpoints with oversized and adversarial property names in CI.
• Maintain dependency inventory so the affected library version can be rapidly located if/when a CVE patch is published.
• Add SBOM-driven alerting for future advisories affecting the parser.

References

• NVD — https://nvd.nist.gov/vuln/detail/CVE-2026-68498
• CWE-400: Uncontrolled Resource Consumption — https://cwe.mitre.org/data/definitions/400.html
• MITRE ATT&CK T1190 — Exploit Public-Facing Application — https://attack.mitre.org/techniques/T1190/
• FIRST EPSS — https://www.first.org/epss/ (CVE-2026-68498 not yet scored)
• CISA KEV Catalog — https://www.cisa.gov/known-exploited-vulnerabilities-catalog (not listed as of this report)

No threat actor campaigns or exploit-in-the-wild evidence are associated with this CVE at this time.