ghost-bits-cast-attack

Name: ghost-bits-cast-attack
Author: Prohao42

91stars8forks

How to install ghost-bits-cast-attack?

prohao42/aimy-skill/ghost-bits-cast-attack

$npx -y skills add Prohao42/aimy-skill --skill ghost-bits-cast-attack

Installs into the current project.

Summary

Java "Ghost Bits" / Cast Attack playbook (Black Hat Asia 2026). Use when attacking Java services where 16-bit char is silently narrowed to 8-bit byte to bypass WAF/IDS for SQL injection, deserialization RCE, file upload (Webshell), path traversal, CRLF injection, request smugglin

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SKILL.md

1	# SKILL: Ghost Bits / Cast Attack — Java char to byte Narrowing Playbook
2
3	> AI LOAD INSTRUCTION: This is a Java-only injection-enabling primitive,
4	> not a standalone vulnerability class. Whenever you see (1) a Java backend,
5	> (2) a WAF/IDS in front of it, and (3) any of {SQLi, deser RCE, file upload,
6	> path traversal, CRLF, request smuggling, SMTP injection} on the menu, ALWAYS
7	> try Ghost Bits variants of the payload before declaring it "blocked". The
8	> root cause is the silent loss of the high 8 bits when Java code narrows a
9	> 16-bit `char` to an 8-bit `byte` — the WAF sees a harmless Unicode
10	> character, the backend reconstructs the original ASCII attack byte. Base
11	> models almost never reach for this primitive.
12	>
13	> Source: Black Hat Asia 2026 talk *Cast Attack: A New Threat Posed by Ghost
14	> Bits in Java* by Xinyu Bai (@b1u3r), Zhihui Chen (@1ue), with contributor
15	> Zongzheng Zheng (@chun_springX).
16
17	## 0. RELATED ROUTING
18
19	Ghost Bits is a bypass primitive that re-enables payloads from many other
20	playbooks. Pair it with whichever attack family applies:
21
22	- [waf-bypass-techniques](../waf-bypass-techniques/SKILL.md) — when a Java
23	backend is suspected and WAF rules block the literal payload, this is the
24	first technique to try beyond classic encoding.
25	- [deserialization-insecure](../deserialization-insecure/SKILL.md) — for
26	Apache Commons BCEL ClassLoader and Fastjson `\u`/`\x` escape variants.
27	- [path-traversal-lfi](../path-traversal-lfi/SKILL.md) — Spring, Jetty,
28	Undertow, Vert.x URL decoding and `%2>` hex folding.
29	- [upload-insecure-files](../upload-insecure-files/SKILL.md) — Tomcat
30	`RFC2231Utility` `filename*` Webshell upload.
31	- [request-smuggling](../request-smuggling/SKILL.md) — Apache HttpClient
32	`<= 4.5.9` (HTTPCLIENT-1974/1978) header CRLF.
33	- [crlf-injection](../crlf-injection/SKILL.md) — Angus Mail / Jakarta Mail
34	SMTP injection and JDK HttpServer response splitting.
35	- [sqli-sql-injection](../sqli-sql-injection/SKILL.md) — Jackson `charToHex`
36	table-lookup truncation hides SQL keywords inside Unicode escapes.
37
38	### Advanced Reference
39
40	Load [PAYLOAD_COOKBOOK.md](./PAYLOAD_COOKBOOK.md) when you need:
41
42	- Full byte-to-Ghost-character lookup table covering every printable ASCII
43	byte 0x20–0x7E and the most useful control bytes (0x00, 0x09, 0x0A, 0x0D).
44	- Per-component affected version matrix and patch identifiers.
45	- Yaklang and Python one-liner payload generators (for `poc.HTTP`,
46	`codec.Encode`, raw socket).
47	- "Multi-view normalization engine" pseudocode for blue-team WAF detection.
48
49	---
50
51	## 1. ONE-MINUTE MENTAL MODEL
52
53	Java's `char` is a 16-bit unsigned integer (UTF-16 code unit). Almost
54	every wire protocol — HTTP/1.1, SMTP, Redis RESP, file paths, raw byte
55	streams — is 8-bit byte oriented. The right way to bridge them is
56	explicit charset encoding:
57
58	```
59	// Correct: explicit UTF-8, multi-byte chars become multi-byte sequences
60	byte[] bytes = str.getBytes(StandardCharsets.UTF_8);
61	out.write(bytes);
62	```
63
64	Tons of legacy code, framework internals, and "fast path" optimizations skip
65	this and silently narrow:
66
67	```
68	// Dangerous: high 8 bits silently dropped
69	byte b = (byte) ch; // 0x966A -> 0x6A
70	out.write(ch); // ByteArrayOutputStream.write(int) keeps low 8 bits
71	dos.writeBytes(str); // DataOutputStream loops char->byte cast
72	int v = ch & 0xFF; // explicit low-byte mask
73	```
74
75	The lost high 8 bits are the Ghost Bits. They turn a multi-byte
76	Unicode character into a single attacker-chosen ASCII byte at the protocol
77	layer.
78
79	```
80	View A (string layer: WAF / business validation / logs)
81	sees: 陪阮严灵瘍瘊 ... "harmless Unicode garbage, allow"
82	\|
83	v silent narrowing somewhere in the call stack
84	View B (byte layer: protocol / file system / parser / class loader)
85	sees: j . % u \r \n ... "executes the dangerous semantics"
86
87	The boundary is breached at the exact moment "view A" and "view B" disagree.
88	```
89
90	Mathematical formulation: to make View B see byte `T`, pick any
91	`k in 0x01..0xFF` and use:
92
93	```
94	c = chr((k << 8) \| T)
95	```
96
97	That gives you 255 candidate Unicode characters per dangerous byte —
98	plenty of room to dodge any signature-based blacklist.
99
100	---
101
102	## 2. THREE ROOT-CAUSE FAMILIES
103
104	The Ghost Bits umbrella covers three distinct underlying bugs. Distinguishing
105	them tells you both which payload shape to send and *what to grep for

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ghost-bits-cast-attack

91stars8forks

View on GitHub

How to install ghost-bits-cast-attack?

prohao42/aimy-skill/ghost-bits-cast-attack

$npx -y skills add Prohao42/aimy-skill --skill ghost-bits-cast-attack

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# SKILL: Ghost Bits / Cast Attack — Java char to byte Narrowing Playbook
2
3	> AI LOAD INSTRUCTION: This is a Java-only injection-enabling primitive,
4	> not a standalone vulnerability class. Whenever you see (1) a Java backend,
5	> (2) a WAF/IDS in front of it, and (3) any of {SQLi, deser RCE, file upload,
6	> path traversal, CRLF, request smuggling, SMTP injection} on the menu, ALWAYS
7	> try Ghost Bits variants of the payload before declaring it "blocked". The
8	> root cause is the silent loss of the high 8 bits when Java code narrows a
9	> 16-bit `char` to an 8-bit `byte` — the WAF sees a harmless Unicode
10	> character, the backend reconstructs the original ASCII attack byte. Base
11	> models almost never reach for this primitive.
12	>
13	> Source: Black Hat Asia 2026 talk *Cast Attack: A New Threat Posed by Ghost
14	> Bits in Java* by Xinyu Bai (@b1u3r), Zhihui Chen (@1ue), with contributor
15	> Zongzheng Zheng (@chun_springX).
16
17	## 0. RELATED ROUTING
18
19	Ghost Bits is a bypass primitive that re-enables payloads from many other
20	playbooks. Pair it with whichever attack family applies:
21
22	- [waf-bypass-techniques](../waf-bypass-techniques/SKILL.md) — when a Java
23	backend is suspected and WAF rules block the literal payload, this is the
24	first technique to try beyond classic encoding.
25	- [deserialization-insecure](../deserialization-insecure/SKILL.md) — for
26	Apache Commons BCEL ClassLoader and Fastjson `\u`/`\x` escape variants.
27	- [path-traversal-lfi](../path-traversal-lfi/SKILL.md) — Spring, Jetty,
28	Undertow, Vert.x URL decoding and `%2>` hex folding.
29	- [upload-insecure-files](../upload-insecure-files/SKILL.md) — Tomcat
30	`RFC2231Utility` `filename*` Webshell upload.
31	- [request-smuggling](../request-smuggling/SKILL.md) — Apache HttpClient
32	`<= 4.5.9` (HTTPCLIENT-1974/1978) header CRLF.
33	- [crlf-injection](../crlf-injection/SKILL.md) — Angus Mail / Jakarta Mail
34	SMTP injection and JDK HttpServer response splitting.
35	- [sqli-sql-injection](../sqli-sql-injection/SKILL.md) — Jackson `charToHex`
36	table-lookup truncation hides SQL keywords inside Unicode escapes.
37
38	### Advanced Reference
39
40	Load [PAYLOAD_COOKBOOK.md](./PAYLOAD_COOKBOOK.md) when you need:
41
42	- Full byte-to-Ghost-character lookup table covering every printable ASCII
43	byte 0x20–0x7E and the most useful control bytes (0x00, 0x09, 0x0A, 0x0D).
44	- Per-component affected version matrix and patch identifiers.
45	- Yaklang and Python one-liner payload generators (for `poc.HTTP`,
46	`codec.Encode`, raw socket).
47	- "Multi-view normalization engine" pseudocode for blue-team WAF detection.
48
49	---
50
51	## 1. ONE-MINUTE MENTAL MODEL
52
53	Java's `char` is a 16-bit unsigned integer (UTF-16 code unit). Almost
54	every wire protocol — HTTP/1.1, SMTP, Redis RESP, file paths, raw byte
55	streams — is 8-bit byte oriented. The right way to bridge them is
56	explicit charset encoding:
57
58	```
59	// Correct: explicit UTF-8, multi-byte chars become multi-byte sequences
60	byte[] bytes = str.getBytes(StandardCharsets.UTF_8);
61	out.write(bytes);
62	```
63
64	Tons of legacy code, framework internals, and "fast path" optimizations skip
65	this and silently narrow:
66
67	```
68	// Dangerous: high 8 bits silently dropped
69	byte b = (byte) ch; // 0x966A -> 0x6A
70	out.write(ch); // ByteArrayOutputStream.write(int) keeps low 8 bits
71	dos.writeBytes(str); // DataOutputStream loops char->byte cast
72	int v = ch & 0xFF; // explicit low-byte mask
73	```
74
75	The lost high 8 bits are the Ghost Bits. They turn a multi-byte
76	Unicode character into a single attacker-chosen ASCII byte at the protocol
77	layer.
78
79	```
80	View A (string layer: WAF / business validation / logs)
81	sees: 陪阮严灵瘍瘊 ... "harmless Unicode garbage, allow"
82	\|
83	v silent narrowing somewhere in the call stack
84	View B (byte layer: protocol / file system / parser / class loader)
85	sees: j . % u \r \n ... "executes the dangerous semantics"
86
87	The boundary is breached at the exact moment "view A" and "view B" disagree.
88	```
89
90	Mathematical formulation: to make View B see byte `T`, pick any
91	`k in 0x01..0xFF` and use:
92
93	```
94	c = chr((k << 8) \| T)
95	```
96
97	That gives you 255 candidate Unicode characters per dangerous byte —
98	plenty of room to dodge any signature-based blacklist.
99
100	---
101
102	## 2. THREE ROOT-CAUSE FAMILIES
103
104	The Ghost Bits umbrella covers three distinct underlying bugs. Distinguishing
105	them tells you both which payload shape to send and *what to grep for

People who liked this also viewed

6 picks

Type