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Fix buffer overflow in wc_HpkeLabeledExtract via oversized ECH #9927

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Fix buffer overflow in wc_HpkeLabeledExtract via oversized ECH #9927

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7 changes: 7 additions & 0 deletions src/ssl_ech.c
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Original file line number Diff line number Diff line change
Expand Up @@ -570,6 +570,13 @@ int SetEchConfigsEx(WOLFSSL_EchConfig** outputConfigs, void* heap,
/* rawLen */
workingConfig->rawLen = length + 4;

/* Reject configs whose raw encoding would overflow the fixed-size
* labeled_ikm buffer in wc_HpkeLabeledExtract */
if (workingConfig->rawLen > MAX_ECH_CONFIG_RAW_SZ) {
ret = BUFFER_E;
break;
}

/* raw body */
workingConfig->raw = (byte*)XMALLOC(workingConfig->rawLen,
heap, DYNAMIC_TYPE_TMP_BUFFER);
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4 changes: 4 additions & 0 deletions src/tls.c
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Expand Up @@ -9986,6 +9986,10 @@ static int TLSX_KeyShare_ProcessPqcHybridClient(WOLFSSL* ssl,
ssl->arrays->preMasterSz = ssSzEcc + ssSzPqc;
}

if (ret != 0) {
ForceZero(ssl->arrays->preMasterSecret, ENCRYPT_LEN);
}

TLSX_KeyShare_FreeAll(ecc_kse, ssl->heap);
TLSX_KeyShare_FreeAll(pqc_kse, ssl->heap);

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15 changes: 15 additions & 0 deletions wolfcrypt/src/hpke.c
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Expand Up @@ -473,6 +473,13 @@ static int wc_HpkeLabeledExtract(Hpke* hpke, byte* suite_id,
WC_ALLOC_VAR_EX(labeled_ikm, byte, MAX_HPKE_LABEL_SZ, hpke->heap,
DYNAMIC_TYPE_TMP_BUFFER, return MEMORY_E);

/* validate total size fits in the labeled_ikm buffer */
if (HPKE_VERSION_STR_LEN + suite_id_len + label_len + ikm_len
> MAX_HPKE_LABEL_SZ) {
WC_FREE_VAR_EX(labeled_ikm, hpke->heap, DYNAMIC_TYPE_TMP_BUFFER);
return BUFFER_E;
}

/* concat the labeled_ikm */
/* version */
XMEMCPY(labeled_ikm, HPKE_VERSION_STR, HPKE_VERSION_STR_LEN);
Expand Down Expand Up @@ -520,6 +527,14 @@ static int wc_HpkeLabeledExpand(Hpke* hpke, byte* suite_id, word32 suite_id_len,
WC_ALLOC_VAR_EX(labeled_info, byte, MAX_HPKE_LABEL_SZ, hpke->heap,
DYNAMIC_TYPE_TMP_BUFFER, return MEMORY_E);

/* validate total size fits in the labeled_info buffer
* total = I2OSP length prefix + version + suite_id + label + info */
if (HPKE_I2OSP_LEN_SZ + HPKE_VERSION_STR_LEN + suite_id_len + label_len
+ infoSz > MAX_HPKE_LABEL_SZ) {
WC_FREE_VAR_EX(labeled_info, hpke->heap, DYNAMIC_TYPE_TMP_BUFFER);
return BUFFER_E;
}

/* copy length */
ret = I2OSP((int)L, 2, labeled_info);
labeled_info_p = labeled_info + 2;
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9 changes: 9 additions & 0 deletions wolfssl/wolfcrypt/hpke.h
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Expand Up @@ -86,6 +86,15 @@ extern const int hpkeSupportedAead[HPKE_SUPPORTED_AEAD_LEN];
#define MAX_HPKE_LABEL_SZ 512
#endif

/* I2OSP encoded length prefix size in LabeledExpand (RFC 9180 Section 4) */
#define HPKE_I2OSP_LEN_SZ 2

/* Maximum raw ECH config length accepted by SetEchConfigsEx. The raw config
* is concatenated into a MAX_HPKE_LABEL_SZ buffer in wc_HpkeLabeledExtract
* along with version (7) + suite_id (HPKE_SUITE_ID_LEN) + label (~12) +
* TLS info prefix (8) overhead. */
#define MAX_ECH_CONFIG_RAW_SZ (MAX_HPKE_LABEL_SZ - 50)
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@philljj philljj Mar 9, 2026

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Where does the - 50 come from?


typedef struct {
void* heap;
word32 kem;
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