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Examples / Report #3395227 Saved analysis

Use of Deprecated strcpy() with User-Controlled Environment Variable in Memory Debug Initialization

curl · 2025-10-2212.3s analysis · $0.015 in model calls

What the report claims

The report claims curl's memory_tracking_init() function uses unsafe strcpy() to copy user-controlled environment variable content into a fixed-size buffer, creating a potential buffer overflow vulnerability.

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

Code contradicts the claim

The code provides evidence against the report's central claim. Review the cited lines before deciding.

curl policy: Debug & Experiments
Why this finding?
  • The code contains a bounds check (line 120) that truncates the user-controlled string to at most 511 characters before the strcpy, guaranteeing the 512-byte destination buffer cannot overflow.
  • The reported 'buffer overflow' is impossible because the source string is shortened to fit the destination before copying.
  • The vulnerable function is compiled only under #ifdef CURLDEBUG (line 111), a debug-only feature; per project policy, '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.'
How this analysis ran 5 claims · 10 citations verified

Checked against curl master on 2025-10-22 (a8f16da71240). Test evaluation split. Citation verification checks that a referenced line was in the evidence; it does not prove the model interpreted it correctly.

1 · Grounding
grounded
no model · 9 references checked out, 0 did not
2 · Claims
NVIDIA-Nemotron-3-Nano-30B-A3B
5 claims · 3327 tokens · $0.0003
3 · Evidence
5 code snippets
real curl source at a8f16da71240
4 · Judgment
Nemotron-3-Ultra-550b-a55b
9391 tokens · 9.5s · $0.0146
5 · Receipts
10 of 10 citations verified
every citation must point at code the judge was shown
Review a draft reply to the reporter

Edit and verify before sending.

Thank you for the detailed report. The code at src/tool_main.c:120-122 shows a bounds check that truncates the environment variable to 511 characters before the strcpy, so the 512-byte buffer cannot overflow. The strcpy is therefore safe in this context. Additionally, this code is only compiled in debug builds (CURLDEBUG), which the project policy excludes from security rewards. No buffer overflow vulnerability exists here.

Inspect all claims and source code 5 claims · 5 code excerpts

Report claims

C1flaw contradicted

uses unsafe strcpy() to copy user-controlled environment variable content into a fixed-size buffer

Read the reasoning

The strcpy is preceded by a bounds check that truncates the source string (env) to at most sizeof(fname)-1 characters, guaranteeing the subsequent strcpy cannot overflow the 512-byte fname buffer. The strcpy is therefore safe in this context, not 'unsafe' as claimed.

src/tool_main.c:120 src/tool_main.c:122
C2location supported

memory_tracking_init() function in src/tool_main.c at line 122

Read the reasoning

The function and line number are correctly identified in the provided source.

src/tool_main.c:112 src/tool_main.c:122
C3trigger supported

CURL_MEMDEBUG environment variable set by user

Read the reasoning

The CURL_MEMDEBUG environment variable is indeed read via curl_getenv and controls the code path.

src/tool_main.c:116
C4impact contradicted

potential buffer overflow leading to memory corruption or arbitrary code execution

Read the reasoning

The bounds check at line 120 ensures the source string length is at most 511 before strcpy, so the 512-byte destination buffer cannot overflow. No buffer overflow, memory corruption, or code execution is possible via this path.

src/tool_main.c:119 src/tool_main.c:120 src/tool_main.c:122
C5reproduction contradicted

set CURL_MEMDEBUG to 600-byte string and run curl to trigger truncation and strcpy

Read the reasoning

Setting CURL_MEMDEBUG to 600 bytes triggers the truncation at line 120, which reduces the string to 511 bytes + null. The subsequent strcpy copies exactly 512 bytes into the 512-byte buffer — no overflow occurs. The proof-of-concept incorrectly assumes strcpy runs on the original 600-byte string.

src/tool_main.c:120 src/tool_main.c:122
Read the original report (excerpt)

Full report on HackerOne ↗

Discovery Method Step 1: Initial Security Scan ``` # Find all files using dangerous string functions find src/ -name "*.c" -exec grep -l "strcpy\|strcat\|sprintf\|gets" {} \; # OUTPUT: # src/tool_progress.c # src/tool_main.c ``` Step 2: Locate Vulnerable Code in Main.c ``` # Find exact strcpy usage in tool_main.c grep -n "strcpy" ./src/tool_main.c # OUTPUT: # 122: strcpy(fname, env); ``` Step 3: Analyze the Vulnerable Function ``` # View complete memory_tracking_init function sed -n '/^static void memory_tracking_init/,/^}/p' ./src/tool_main.c ``` Vulnerable Function Found: ``` static void memory_tracking_init(void) { char *env; /* if CURL_MEMDEBUG is set, this starts memory tracking message logging */ env = curl_getenv("CURL_MEMDEBUG"); if(env) { /* use the value as filename */ char fname[512]; if(strlen(env) >= sizeof(fname)) env[sizeof(fname)-1] = '\0'; // Truncation occurs strcpy(fname, env); // ⚠️ VULNERABLE LINE 122 curl_free(env); curl_dbg_memdebug(fname); } } ``` Step 4: Analyze Input Source ``` # Find environment variable usage grep -n "CURL_MEMDEBUG" ./src/tool_main.c # OUTPUT confirms user-controlled input source ``` Step 5: Buffer Declaration Analysis ``` # Find fname buffer declaration grep -B 10 "strcpy(fname, env)" ./src/tool_main.c | grep -E "char.*fname" # OUTPUT: # char fname[512]; ``` Vulnerability Description Root Cause The memory_tracking_init() function in src/tool_main.c at line 122 uses unsafe strcpy() to copy user-controlled environment variable content into a fixed-size buffer. This represents a critical security best practice violation with actual exploit potential. Technical Analysis ``` // VULNERABLE CODE PATTERN: char fname[512]; // Fixed 512-byte buffer env = curl_getenv("CURL_MEMDEBUG"); // USER-CONTROLLED INPUT if(strlen(env) >= sizeof(fname)) env[sizeof(fname)-1] = '\0'; // Dangerous truncation strcpy(fname, env); // LINE 122: UNSAFE strcpy() ``` Critical Security Issues strcpy() Usage - Deprecated and inherently unsafe function User-Controlled Input - Environment variable attacker controlled Truncation Flaw - Modifies original environment variable Fixed Buffer - No dynamic allocation based on input size ## Impact Security Impact CVSS Score: 6.5 (Medium-High) Attack Vector: Local (Environment Variable) Attack Complexity …

Source code

src/tool_main.clines 97–147 · lines 122-122 cited by the report
97static int main_checkfds(void)
98{
99 int fd[2];
100 while((fcntl(STDIN_FILENO, F_GETFD) == -1) ||
101 (fcntl(STDOUT_FILENO, F_GETFD) == -1) ||
102 (fcntl(STDERR_FILENO, F_GETFD) == -1))
103 if(pipe(fd))
104 return 1;
105 return 0;
106}
107#else
108#define main_checkfds() 0
109#endif
110
111#ifdef CURLDEBUG
112static void memory_tracking_init(void)
C2: static void memory_tracking_init(void) at line 112
113{
114 char *env;
115 /* if CURL_MEMDEBUG is set, this starts memory tracking message logging */
116 env = curl_getenv("CURL_MEMDEBUG");
C3: env = curl_getenv("CURL_MEMDEBUG"); reads user-controlled environment variable
117 if(env) {
118 /* use the value as filename */
119 char fname[512];
C4: char fname[512]; declares 512-byte destination buffer
120 if(strlen(env) >= sizeof(fname))
C1: Bounds check: if(strlen(env) >= sizeof(fname)) env[sizeof(fname)-1] = '\0'; ensures source string fits in destination buffer before strcpy
C4: if(strlen(env) >= sizeof(fname)) env[sizeof(fname)-1] = '\0'; truncates source to fit
C5: Truncation logic modifies env to max 511 chars before strcpy
121 env[sizeof(fname)-1] = '\0';
122 strcpy(fname, env);
C1: strcpy(fname, env) copies at most 512 bytes (511 chars + null) into fname[512] after truncation
C2: strcpy(fname, env) at line 122
C4: strcpy(fname, env) copies truncated source into destination
C5: strcpy operates on already-truncated source
123 curl_free(env);
124 curl_dbg_memdebug(fname);
125 /* this weird stuff here is to make curl_free() get called before
126 curl_dbg_memdebug() as otherwise memory tracking will log a free()
127 without an alloc! */
128 }
129 /* if CURL_MEMLIMIT is set, this enables fail-on-alloc-number-N feature */
130 env = curl_getenv("CURL_MEMLIMIT");
131 if(env) {
132 curl_off_t num;
133 const char *p = env;
134 if(!curlx_str_number(&p, &num, LONG_MAX))
135 curl_dbg_memlimit((long)num);
136 curl_free(env);
137 }
138}
139#else
140# define memory_tracking_init() tool_nop_stmt
141#endif
142
143/*
144** curl tool main function.
145*/
146#if defined(_UNICODE) && !defined(UNDER_CE)
147#if defined(__GNUC__) || defined(__clang__)
lib/memdebug.clines 78–93 · definition of curl_dbg_memdebug
78void curl_dbg_memdebug(const char *logname)
79{
80 if(!curl_dbg_logfile) {
81 if(logname && *logname)
82 curl_dbg_logfile = CURLX_FOPEN_LOW(logname, FOPEN_WRITETEXT);
83 else
84 curl_dbg_logfile = stderr;
85#ifdef MEMDEBUG_LOG_SYNC
86 /* Flush the log file after every line so the log is not lost in a crash */
87 if(curl_dbg_logfile)
88 setbuf(curl_dbg_logfile, (char *)NULL);
89#endif
90 }
91 if(!registered_cleanup)
92 registered_cleanup = !atexit(curl_dbg_cleanup);
93}
lib/memdebug.c@curl-8_16_0lines 77–96 · definition of curl_dbg_memdebug as in release curl-8_16_0; differs from master; commits that changed it since: 20142f5d06 build: avoid overriding system symbols for fopen functions
Show 20 lines (not cited by the judge)
77void curl_dbg_memdebug(const char *logname)
78{
79 if(!curl_dbg_logfile) {
80 if(logname && *logname)
81#ifdef CURL_FOPEN
82 curl_dbg_logfile = CURL_FOPEN(logname, FOPEN_WRITETEXT);
83#else
84 curl_dbg_logfile = (fopen)(logname, FOPEN_WRITETEXT);
85#endif
86 else
87 curl_dbg_logfile = stderr;
88#ifdef MEMDEBUG_LOG_SYNC
89 /* Flush the log file after every line so the log is not lost in a crash */
90 if(curl_dbg_logfile)
91 setbuf(curl_dbg_logfile, (char *)NULL);
92#endif
93 }
94 if(!registered_cleanup)
95 registered_cleanup = !atexit(curl_dbg_cleanup);
96}
lib/escape.clines 198–201 · definition of curl_free
Show 4 lines (not cited by the judge)
198void curl_free(void *p)
199{
200 free(p);
201}
lib/getenv.clines 77–80 · definition of curl_getenv
Show 4 lines (not cited by the judge)
77char *curl_getenv(const char *v)
78{
79 return GetEnv(v);
80}