vulnerability / NVI-00017705 / Revision 1
MessagePack-CSharp: Unity unsafe blit formatter allocates from unbounded byte length
GitHub lists this reviewed advisory for MessagePack, MessagePack. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
MessagePack
source listed< 2.5.301
## Summary `UnsafeBlitFormatterBase.Deserialize` reads an attacker-controlled `byteLength` from an extension payload and allocates an array based on that value before validating it against the extension header length or remaining payload bytes. The outer extension header is bounded by available input, but that bound is not used to constrain the inner `byteLength` before allocation. A very small payload can therefore request a very large `T[]` allocation. ## Impact Applications are affected when they deserialize untrusted payloads using Unity blit resolvers such as `UnityBlitResolver` or `UnityBlitWithPrimitiveArrayResolver`. This is especially relevant to Unity multiplayer clients or servers that use MessagePack-CSharp for networked values such as vectors, matrices, or primitive arrays. A hostile peer can send an extension payload with a large declared byte length and cause an out-of-memory exception or process termination on memory-constrained platforms. The resolver is opt-in, but the vulnerable value is pure wire input and the allocation happens before the formatter verifies that the declared bytes are actually present in the extension body. ## Affected components - P
MessagePack
source listed>= 3.0, < 3.1.7
## Summary `UnsafeBlitFormatterBase.Deserialize` reads an attacker-controlled `byteLength` from an extension payload and allocates an array based on that value before validating it against the extension header length or remaining payload bytes. The outer extension header is bounded by available input, but that bound is not used to constrain the inner `byteLength` before allocation. A very small payload can therefore request a very large `T[]` allocation. ## Impact Applications are affected when they deserialize untrusted payloads using Unity blit resolvers such as `UnityBlitResolver` or `UnityBlitWithPrimitiveArrayResolver`. This is especially relevant to Unity multiplayer clients or servers that use MessagePack-CSharp for networked values such as vectors, matrices, or primitive arrays. A hostile peer can send an extension payload with a large declared byte length and cause an out-of-memory exception or process termination on memory-constrained platforms. The resolver is opt-in, but the vulnerable value is pure wire input and the allocation happens before the formatter verifies that the declared bytes are actually present in the extension body. ## Affected components - P
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-w567-gjr2-hm5j ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.