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Graph/premature-read-before-bounds-check

AntiPattern

Premature Read Before Bounds

premature-read-before-bounds-check

Decoders and parsers perform reads or pointer advancement before validating remaining buffer size, causing stack exhaustion or crashes when inputs are oversized or truncated. The stake is reliability and potential denial of service during parsing.

Node Details

Public graph metadata

Updated5/30/2026

Connections

30 linked nodes

MATCHESSolution

Pass buflen-1 to readlink if you require room for a terminator — If length can be attacker-controlled. Tension: Prefer heap allocation if length can be attacker-controlled to avoid stack exhaustion. Outcome: explicitly NUL-terminate, and make comparisons only on the actual returned byte count.

MATCHESSolution

Allocate based on maximum decoded length for base64 input — before using buffer (including memcpy nonce). Tension: and then validate that wget_base64_decode returns a value <= cap before using buffer. Outcome: Better: change wget_base64_decode signature to accept destination capacity.

MATCHESSolution

Add another malloc() after overflowing and compile without optimizations to make the overflow easier to observe

MATCHESSolution

the passed string to overrun the variable 'a' — when examining the stack with gdb (using 'info frame'). Tension: it doesn't happen. Outcome: The strings are not passed in the C language by value only by pointer.

MATCHESSolution

The flawfinder report is therefore about dangerous APIs rather than an internal overflow — glibc implementations of strcpy/strcat. Tension: bounds checks cannot be added without changing the API.

MATCHESSolution

If you don't care about the bytes read and just want the digest. Outcome: byte[] buffer = new byte[2048]; while (digestInputStream.read(buffer) >= 0);.

MATCHESSolution

Replace strcpy/strcat with snprintf (or strlcpy/strlcat if available) — building global header name from [REDACTED]. Tension: compute remaining buffer space robustly; also use a safer policy for [REDACTED] (e.g., cap length). Outcome: Add overflow checks when computing allocation size.

MATCHESSolution

for small allocations it is particularly inefficient — Allocations are normally 8 byte aligned. Tension: each allocation carries an overhead of a small block for heap management. Outcome: at least 8 bytes to maintain alignment.

MATCHESSolution

adding `where <= lim - 2` guard. Tension: This ensures at least 2 bytes remain (the sign/prefix byte + at least 1 data byte) before entering the base-256 decoder. Outcome: Fixed in GNU tar release_1_35 (commit 3da7840, Feb 11 2023).

MATCHESSolution

Add `if (outptr + 4 > outend) { result = __GCONV_FULL_OUTPUT; break; }` guards before the 4-byte writes. Tension: the SS2/SS3 branches never got the same treatment. Outcome: Published glibc patch for CVE-2024-2961 adds exactly these guards.

MATCHESSolution

Add check after strtol call: `if (remaining_chunk_size < 0) { return false; }`. Tension: negative not validated before use as read() size. Outcome: wget 1.19.2 added validation of chunk size sign.

MATCHESSolution

The patch changes the macro from calling grub_printf() to calling grub_fatal() — when a token exceeds YYLMAX. Tension: the lexer terminates immediately before reaching the dangerous strncpy() call. Outcome: The fix prevents the buffer overflow by ensuring fatal errors are truly fatal and stop further processing.

MATCHESSolution

Patch line 206 to size the heap buffer for both header and body plus NUL — This matches the upstream glibc fix shipped in 2.39. Tension: the full formatted message lives in the heap buffer. Outcome: Set `bufsize = l + vl`.

MATCHESSolution

Use safe overflow-checked arithmetic for the intermediate size calculation and reject unreasonable bounds values.

MATCHESSolution

unbounded memory allocation (DoS) — processing a crafted ELF file.

MATCHESSolution

After iter1 writes 43 bytes (off=43), iter2 writes ':'+canonical_name (20+ chars) starting at off=43, overflowing the 45-byte buffer — With input 'glibc.malloc.mxfast=glibc.malloc.mxfast=512' (43 bytes), the buffer is 45 bytes. Tension: overflowing the 45-byte buffer. Outcome: Verified by examining fix commit 1056e5b4c3.

MATCHESSolution

Located wordexp.c in posix/ directory. Tension: Found vulnerable arithmetic at line 160 in w_addword. Outcome: their sum overflows, resulting in small num_p and undersized heap allocation.

MATCHESSolution

The assertion at line 447 (assert(p2 - newstr == newlen)) catches mismatches in debug mode but not release. — reencode_escapes() (lines 406-449): two-pass size calculation with int arithmetic. Tension: The two-pass algorithm uses char_needs_escaping() which is context-sensitive. Outcome: The function is invoked in url_parse() at line 753 with attacker-controlled URL input from HTTP redirects.

MATCHESSolution

NO upper-bound check exists. — With XML_PARSE_HUGE enabled. Outcome: heap OOB write.

MATCHESSolution

Never cache raw pointers into a buffer that may be reallocated.

MATCHESSolution

Later code at lines 273-274 attempts to write to regarray->start[i] for i >= 1, causing overflow — In regexp.c lines 265-267 within match_regex. Tension: Only allocates 1 element. Outcome: regsize can reach 16 (when max_id is 15).

MATCHESSolution

Fix 1: In parser.c xmlParseCharData, change `int nbchar` to `ptrdiff_t nbchar`. Tension: to prevent truncation of large pointer differences.

MATCHESSolution

Replace the condition at line 773-775 — in binutils/dwarf.c in the fetch_indexed_string() function. Tension: checking 'curr + length < (end - 8/16)'. Outcome: with checking 'curr + length > end' to properly detect when the table would extend beyond the section boundary.

MATCHESSolution

Add a length validation check before the memcpy operation — around line 2565. Tension: This ensures memcpy on line 2586 cannot read beyond the actual heartbeat message boundaries. Outcome: if (payload > s->s3->rrec.length - 3) { SSLerr(...); return 0; }.

MATCHESSolution

Fix in src/iri.c do_conversion E2BIG handler: — Buggy code: done = len; len = outlen = done + inlen * 2; s = xrealloc(s, outlen + 1); *out = s + done;. Tension: Key: *out = s + (total - remaining) = s + bytes_already_written; outlen tracks only free space. Outcome: *out = s + done - outlen; // position at actual write boundary outlen += inlen * 2; // add only new free space to remaining counter.

MATCHESSolution

Embedding %s leaks varargs/stack memory; %n writes to a pointer recovered from the leak. — upd_wrtrtl at line 6994. Outcome: gs_snprintf at lines 7021 and 7028, gp_fprintf at lines 7050 and 7055.

MATCHESSolution

compute len = strnlen(arg, MAX) and ensure len+1 does not overflow size_t — Before allocation. Tension: check board != NULL before copying. Outcome: If allocation fails, return an error code to the caller.

MATCHESSolution

Use size_t for all length calculations — src/http.c parse_content_disposition(). Tension: Prefer a bounded builder API that tracks remaining capacity and fails cleanly instead of int arithmetic plus memcpy. Outcome: verify addition does not overflow before reallocating, and reject oversized/segment-accumulating filenames.

MATCHESSolution

Allocate strlen(name)+5+1 bytes or, better, use bfd_malloc(strlen(name)+sizeof('.plt')). Tension: copy with memcpy/snprintf into a bounded buffer. Outcome: Also check bfd_malloc return before use.

MATCHESSolution

Page instead: use `--limit 15` and walk backwards with `--before <lowest message id from the previous page>` — Each page stays well under the 64KB stdout boundary. Tension: Do not raise --limit to cover a large read. Outcome: As a defensive check, assert the captured stdout parses as JSON before use rather than trusting the exit code.

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