Jackson CBOR Parser DoS via Unbounded TagList Growth (2.18.2)
CVE-2026-106554 Published on November 4, 2026
jackson-dataformat-cbor: quadratic-time TagList growth on unbounded stacked tags (CPU/GC DoS, PoC)
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).
Timeline
GHSA-cjg7-h3pr-p927 published in FasterXML/jackson-dataformats-binary
Weakness Type
Inefficient Algorithmic Complexity
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
Products Associated with CVE-2026-106554
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Affected Versions
FasterXML jackson-dataformat-cbor:- Version 2.15.0 and below 2.18.12 is affected.
- Version 2.18.12 is unaffected.
- Version 2.19.0 and below 2.21.8 is affected.
- Version 2.21.8 is unaffected.
- Version 2.22.0 and below 2.22.4 is affected.
- Version 2.22.4 is unaffected.
- Version 3.0.0 and below 3.1.8 is affected.
- Version 3.1.8 is unaffected.
- Version 3.2.0 and below 3.2.4 is affected.
- Version 3.2.4 is unaffected.