Guard against sizes that do not fit in an int
What the developer wrote
Authored by Salvatore Ingala
Guard against sizes that do not fit in an int
What changed, and why it matters
This commit adds a safety check in the Ledger Bitcoin app's code that handles BIP32 derivation paths extracted from a PSBT (Partially Signed Bitcoin Transaction). The change prevents a very large, attacker-chosen data length from being silently truncated when converted from a large unsigned integer (size_t) to a signed integer (int). Such truncation could theoretically cause the app to allocate or read/write the wrong amount of memory, potentially leading to crashes or memory corruption. The patch is narrow and defensive, but it does not show a complete exploit path.
Review the full call chain to ensure cs->result = -1 is properly propagated and causes the signing operation to abort safely. Consider adding unit tests with oversized PSBT fields and verify no other size_t-to-int conversions exist in the PSBT handler code.
Security signals we found
Integer truncation / signedness issue between size_t and int
Memory safety hardening in PSBT parsing path
Defensive bounds check added in callback
Potential denial-of-service or memory corruption vector in BIP32 derivation extraction
Evidence from the diff
In src/handler/sign_psbt/extract_bip32_derivation.c, the fpt_der_data_len_callback receives a size_t data_length and previously assigned it directly to an int field (total_data_length) in the callback state. On platforms where size_t is wider than int, a maliciously large data_length would be truncated. The patch guards against this by checking if data_length exceeds INT_MAX, setting cs->result = -1 and returning early. This is a partial hardening measure; the commit does not show how the result field is consumed downstream or whether callers actually abort on error.
Changed components
src/handler/sign_psbt/extract_bip32_derivation.cLedger Bitcoin app PSBT signing flowBIP32 derivation path extractionInspect captured patch +10 / −1
diff --git a/src/handler/sign_psbt/extract_bip32_derivation.c b/src/handler/sign_psbt/extract_bip32_derivation.c
index 1cd5d9a..2976464 100644
--- a/src/handler/sign_psbt/extract_bip32_derivation.c
+++ b/src/handler/sign_psbt/extract_bip32_derivation.c
@@ -1,5 +1,6 @@
#include <stdint.h>
#include <string.h>
+#include <limits.h>
#include "extract_bip32_derivation.h"
@@ -21,7 +22,15 @@ typedef struct {
} fpt_der_callback_data_t;
static void fpt_der_data_len_callback(size_t data_length, void *callback_state) {
- ((fpt_der_callback_data_t *) callback_state)->total_data_length = data_length;
+ fpt_der_callback_data_t *cs = (fpt_der_callback_data_t *) callback_state;
+
+ if (data_length > INT_MAX) {
+ // fail early if the conversion to int would overflow
+ // by setting the error result in the callback state
+ cs->result = -1;
+ return;
+ }
+ cs->total_data_length = data_length;
}
static void fpt_der_data_callback(buffer_t *data, void *callback_state) {
Why this scored 58/100
Community notes
Notes can correct, qualify, or add evidence to the AI analysis. Every note shown here has been validated by a human moderator.
The AI analysis stands alone for now. Submit a note if you can add evidence or important context.