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| Code Block | ||||
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#include <stddef.h>
#include <stdio.h>
void f(FILE *file) {
enum { BUFFER_SIZE = 1024 };
wchar_t wbuf[BUFFER_SIZE];
const size_t size = sizeof(*wbuf);
const size_t nitems = sizeof(wbuf) / size;
size_t nread = fread(wbuf, size, nitems, file);
/* ... */
} |
Noncompliant Code Example (Heartbleed)
CERT vulnerability 720951 describes a vulnerability in OpenSSL versions 1.0.1 through 1.0.1f, popularly known as "Heartbleed". This vulnerability allows a malicious packet fed to a server using OpenSSL to trick that server into returning up to 64 kilobytes of its internal memory. This memory can contain sensitive information, including cryptographic keys, usernames and passwords.
The vulnerable code appears below:
int dtls1_process_heartbeat(SSL *s) { unsigned char *p = &s->s3->rrec.data[0], *pl; unsigned short hbtype; unsigned int payload; unsigned int padding = 16; /* Use minimum padding */ /* Read type and payload length first */ hbtype = *p++; n2s(p, payload); pl = p; /* ... More code ... */ if (hbtype == TLS1_HB_REQUEST) { unsigned char *buffer, *bp; int r; /* Allocate memory for the response, size is 1 byte * message type, plus 2 bytes payload length, plus * payload, plus padding */ buffer = OPENSSL_malloc(1 + 2 + payload + padding); bp = buffer; /* Enter response type, length and copy payload */ *bp++ = TLS1_HB_RESPONSE; s2n(payload, bp); memcpy(bp, pl, payload); /* ... More code ... */ } /* ... More code ... */} |
This code processes a 'heartbeat' packet from a client. As specified in RFC 6520, when the program receives a heartbeat packet, it must echo the packet's data back to the client. In addition to the data, the packet contains a length field that conventionally indicates the number of bytes in the packet data, but there is nothing to prevent a malicious packet from lying about its data length.
The p pointer, along with payload and p1 contain data from a packet. The code allocates a buffer sufficient to contain payload bytes, with some overhead, and copies payload bytes starting at p1 into this buffer, and sends it to the client. Notably absent are any checks that payload actually indicates the correct size of the memory. Because an attacker can specify an arbitrary value for payload, she can cause this routine to read and return memory beyond the block allocated to p, which violates INT04-C. Enforce limits on integer values originating from tainted sources. In this case, the call to memcpy() would create a pointer that does not lie within the bounds of the character array.
Compliant Solution (Heartbleed)
OpenSSL version 1.0.1g contains the following patch, which guarantees that payload is within a valid range. The range is limited by the size of the input record.
int dtls1_process_heartbeat(SSL *s) { unsigned char *p = &s->s3->rrec.data[0], *pl; unsigned short hbtype; unsigned int payload; unsigned int padding = 16; /* Use minimum padding */ /* ... More code ... */ /* Read type and payload length first */ if (1 + 2 + 16 > s->s3->rrec.length) return 0; /* silently discard */ hbtype = *p++; n2s(p, payload); if (1 + 2 + payload + 16 > s->s3->rrec.length) return 0; /* silently discard per RFC 6520 */ pl = p; /* ... More code ... */ if (hbtype == TLS1_HB_REQUEST) { unsigned char *buffer, *bp; int r; /* Allocate memory for the response, size is 1 byte * message type, plus 2 bytes payload length, plus * payload, plus padding */ buffer = OPENSSL_malloc(1 + 2 + payload + padding); bp = buffer; /* Enter response type, length and copy payload */ *bp++ = TLS1_HB_RESPONSE; s2n(payload, bp); memcpy(bp, pl, payload); /* ... More code ... */ } /* ... More code ... */} |
Risk Assessment
Depending on the library function called, an attacker may be able to use a heap or stack overflow vulnerability to run arbitrary code.
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| Coverity | 6.5 | BUFFER_SIZE | Fully Implemented | ||||||||
5.0 |
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| ABR |
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| PRQA QA-C |
| 2931 | Fully implemented | ||||||||
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Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
CERT vulnerability note VU#720951 describes a vulnerability in OpenSSL versions 1.0.1 through 1.0.1f, popularly known as "Heartbleed." For a fuller description of this vulnerability, see the Related Vulnerabilities section of INT04-C. Enforce limits on integer values originating from tainted sources.
Related Guidelines
| C Secure Coding Standard | API00-C. Functions should validate their parameters ARR01-C. Do not apply the sizeof operator to a pointer when taking the size of an array INT30-C. Ensure that unsigned integer operations do not wrap |
| ISO/IEC TS 17961:2013 | Forming invalid pointers by library functions [libptr] |
| ISO/IEC TR 24772:2013 | Buffer Boundary Violation (Buffer Overflow) [HCB] |
| MITRE CWE
| CWE-119, Improper Restriction of Operations within the Bounds of a Memory Buffer |
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