CVE-2026-63126 Wire: Unauthenticated decoder crash via 32-bit length integer overflow in ByteArrayProtoReader32 (incomplete fix of CVE-2026-45799)
An attacker can cause a denial of service in the Wire protobuf library by sending malformed data that triggers an integer overflow, leading to crashes or excessive allocation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-63126?
CVE-2026-63126 is a high-severity vulnerability in square wire, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-190
Which versions are affected by CVE-2026-63126?
4 open source packages ship an affected version, including com.squareup.wire:wire-runtime.
| Package | Affected | Fixed in |
|---|---|---|
com.squareup.wire:wire-runtime Maven | All versions | 6.4.5 |
com.squareup.wire:wire-runtime Maven | All versions | 6.4.5 |
com.squareup.wire:wire-runtime Maven | From 7.0.0-alpha01 | 7.0.0-alpha04 |
com.squareup.wire:wire-runtime Maven | From 7.0.0-alpha01 | 7.0.0-alpha04 |
How do I fix CVE-2026-63126?
Upgrade com.squareup.wire:wire-runtime to a fixed version for your release line: 6.4.5 or 7.0.0-alpha04.
Is CVE-2026-63126 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-63126 exists.
Sources
Also known as GHSA-9rm7-3qhh-h2mc.