---
id: "CVE-2026-106554"
kind: "vulnerability"
aliases: ["CVE-2026-106554"]
title: "Jackson CBOR parser: stacked tags cause quadratic CPU and memory use"
severity: "medium"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["backend", "cbor", "jackson", "java", "package"]
not_affected_if: ["no-untrusted-cbor-input"]
published_at: "2026-11-04T16:17:32+00:00"
first_seen_at: "2026-11-04T16:28:10+00:00"
updated_at: "2026-11-04T16:29:02+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-106554", "first_seen_at": "2026-11-04T16:28:10+00:00"}]
---

# Jackson CBOR parser: stacked tags cause quadratic CPU and memory use

A crafted CBOR input with a long run of semantic tags makes jackson-dataformat-cbor grow its tag list in fixed steps, so parsing time grows quadratically. An attacker can tie up request threads and garbage collection with a modest payload.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the version of `com.fasterxml.jackson.dataformat:jackson-dataformat-cbor` in your dependency tree, for example with `mvn dependency:tree` or `gradle dependencies`.
- Look for CBOR parsing of untrusted input in request handlers.

## Timeline

- 2026-11-04T16:28:10+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-106554

## Documents

- [advisory] Vendor advisory: github.com https://github.com/FasterXML/jackson-dataformats-binary/security/advisories/GHSA-cjg7-h3pr-p927

## From the sources

One CBOR-parsing issue in jackson-dataformats-binary's CBOR module: an unbounded run of CBOR tags drives quadratic-time TagList growth (CPU/GC-exhaustion DoS, PoC-proven).



PoC executed against com.fasterxml.jackson.dataformat:jackson-dataformat-cbor:2.18.2; present in current 2.x and 3.x (tools.jackson.dataformat.cbor) HEAD. Distinct from the Avro and Smile/Protobuf advisories for this repo.



Quadratic CPU/GC DoS from an unbounded chain of CBOR tags (PoC-proven). File: cbor/src/main/java/.../cbor/CBORParser.java (tag handling -> TagList).



CBOR permits a data item to be preceded by any number of semantic tags. The CBOR parser accumulates them in a TagList whose backing array grows by a fixed increment (+8), not by doubling, and re-scans/copies on each growth. An attacker sends a value preceded by a long run of tag bytes; the fixed-increment growth makes accumulating N tags O(N^2) in time (plus GC pressure), with no cap on the number of stacked tags.



PoC (executed, JDK 17): feeding a CBOR stream consisting of a long run of tag bytes (e.g. tag 0xC0+) before a trivial value forces quadratic CPU/GC; parse time grows super-linearly with the tag count, pinning a request thread with no configurable limit.



Impact. Algorithmic-complexity denial of service (CWE-407): a modest input of stacked tags consumes quadratic CPU/GC, pinning a request thread; concurrent requests exhaust the pool.



Fix. Grow TagList by doubling and/or cap the number of stacked tags (StreamReadConstraints-style).

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