# Integer Overflow (Web Applications)

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> Ukurasa huu unaelezea jinsi ambapo **integer overflows/truncations zinaweza kutumiwa katika web applications na browsers**.  Kwa exploitation primitives ndani ya native binaries unaweza endelea kusoma ukurasa maalum:
>
>
{{#ref}}
> ../../binary-exploitation/integer-overflow-and-underflow.md
> {{#endref}}

---

## 1. Why integer math still matters on the web

Licha ya kwamba sehemu kubwa ya business-logic katika modern stacks imeandikwa kwa lugha za *memory-safe*, runtime inayofanya kazi chini yake (au third-party libraries) hatimaye imeimplemented katika C/C++. Wakati wowote nambari zinazoathiriwa na user zinapotumika kugawa buffers, kuhesabu offsets, au kufanya ukaguzi wa urefu, **wrap-around ya 32-bit au 64-bit inaweza kubadilisha parameter inayotarajiwa kuwa isiyo hatari kuwa out-of-bounds read/write, logic bypass au DoS**.

Typical attack surface:

1. **Numeric request parameters** – classic id, offset, or count fields.
2. **Length / size headers** – Content-Length, WebSocket frame length, HTTP/2 continuation_len, etc.
3. **File-format metadata parsed server-side or client-side** – image dimensions, chunk sizes, font tables.
4. **Language-level conversions** – signed↔unsigned casts in PHP/Go/Rust FFI, JS Number → int32 truncations inside V8.
5. **Authentication & business logic** – coupon value, price, or balance calculations that silently overflow.

---

## 2. Recent real-world vulnerabilities (2023-2025)

| Mwaka | Komponenti | Sababu kuu | Athari |
|------|-----------|-----------|--------|
| 2023 | **libwebp – CVE-2023-4863** | 32-bit multiplication overflow when computing decoded pixel size | Ilisababisha Chrome 0-day (BLASTPASS on iOS), ikaruhusu *remote code execution* ndani ya renderer sandbox.  |
| 2024 | **V8 – CVE-2024-0519** | Truncation to 32-bit when growing a JSArray leads to OOB write on the backing store | Remote code execution baada ya kutembelea mara moja.  |
| 2025 | **Apollo GraphQL Server** (unreleased patch) | 32-bit signed integer used for first/last pagination args; negative values wrap to huge positives | Logic bypass & memory exhaustion (DoS). |

---

## 3. Testing strategy

### 3.1 Boundary-value cheat-sheet

Tuma **extreme signed/unsigned values** kila mahali ambapo integer inatarajiwa:
```
-1, 0, 1,
127, 128, 255, 256,
32767, 32768, 65535, 65536,
2147483647, 2147483648, 4294967295,
9223372036854775807, 9223372036854775808,
0x7fffffff, 0x80000000, 0xffffffff
```
Mifomato mingine muhimu:
* Hex (0x100), octal (0377), scientific (1e10), JSON big-int (9999999999999999999).
* Mfuatano mrefu sana wa tarakimu (>1kB) ili kugonga custom parsers.

### 3.2 Kiolezo cha Burp Intruder
```
§INTEGER§
Payload type: Numbers
From: -10 To: 4294967300 Step: 1
Pad to length: 10, Enable hex prefix 0x
```
### 3.3 Fuzzing libraries & runtimes

* **AFL++/Honggfuzz** pamoja na libFuzzer harness karibu na parser (kwa mfano, WebP, PNG, protobuf).
* **Fuzzilli** – grammar-aware fuzzing ya JavaScript engines ili kugonga V8/JSC integer truncations.
* **boofuzz** – network-protocol fuzzing (WebSocket, HTTP/2) ikilenga length fields.

---

## 4. Exploitation patterns

### 4.1 Logic bypass katika server-side code (mfano wa PHP)
```php
$price = (int)$_POST['price'];          // expecting cents (0-10000)
$total = $price * 100;                  // ← 32-bit overflow possible
if($total > 1000000){
die('Too expensive');
}
/* Sending price=21474850 → $total wraps to ‑2147483648 and check is bypassed */
```
### 4.2 Heap overflow via image decoder (libwebp 0-day)
WebP lossless decoder ilizidisha image width × height × 4 (RGBA) ndani ya 32-bit int. Faili iliyotengenezwa kwa vipimo 16384 × 16384 iliresulta overflows kwenye multiplication, allocates short buffer na baadaye ikaandika **~1GB** ya decompressed data past the heap – ikisababisha RCE katika every Chromium-based browser kabla ya 116.0.5845.187.

### 4.3 Browser-based XSS/RCE chain
1. **Integer overflow** in V8 gives arbitrary read/write.
2. Escape the sandbox with a second bug or call native APIs to drop a payload.
3. The payload then injects a malicious script into the origin context → stored XSS.

---

## 5. Defensive guidelines

1. **Use wide types or checked math** – e.g., size_t, Rust checked_add, Go math/bits.Add64.
2. **Validate ranges early**: kataa thamani yoyote nje ya business domain kabla ya arithmetic.
3. **Enable compiler sanitizers**: -fsanitize=integer, UBSan, Go race detector.
4. **Adopt fuzzing in CI/CD** – waunganishe coverage feedback na boundary corpora.
5. **Stay patched** – browser integer overflow bugs mara nyingi zinatumiwa ndani ya wiki.

---



## References

* [NVD CVE-2023-4863 – libwebp Heap Buffer Overflow](https://nvd.nist.gov/vuln/detail/CVE-2023-4863)
* [Google Project Zero – "Understanding V8 CVE-2024-0519"](https://googleprojectzero.github.io/)
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