From: Jakub Szczudlo (Nokia) <[email protected]> Backport patch to fix CVE-2026-5419.
References: https://nvd.nist.gov/vuln/detail/CVE-2026-5419 Upstream fix: https://gitlab.com/gnutls/gnutls/-/commit/1e627aa5ad95c6dc0518d94e9a009997b081a1ab Tested with ptes Signed-off-by: Jakub Szczudlo <[email protected]> Signed-off-by: Yoann Congal <[email protected]> [YC: fixed patch unneeded changes] --- .../gnutls/gnutls/CVE-2026-5419.patch | 248 ++++++++++++++++++ meta/recipes-support/gnutls/gnutls_3.8.12.bb | 1 + 2 files changed, 249 insertions(+) create mode 100644 meta/recipes-support/gnutls/gnutls/CVE-2026-5419.patch diff --git a/meta/recipes-support/gnutls/gnutls/CVE-2026-5419.patch b/meta/recipes-support/gnutls/gnutls/CVE-2026-5419.patch new file mode 100644 index 00000000000..714814eee2c --- /dev/null +++ b/meta/recipes-support/gnutls/gnutls/CVE-2026-5419.patch @@ -0,0 +1,248 @@ +From 2f3732538d7d8e1ae255ca68c20efc61a1d5b3e2 Mon Sep 17 00:00:00 2001 +From: Daiki Ueno <[email protected]> +Date: Fri, 4 Sep 2026 09:17:32 +0000 +Subject: [PATCH] gnutls_cipher_decrypt3: make PKCS#7 unpadding branch free + +This tries to make the logic of PKCS#7 padding removal constant-time, +by removing potential branching operations. + +CVE: CVE-2026-5419 +Upstream-Status: Backport [https://gitlab.com/gnutls/gnutls/-/commit/1e627aa5ad95c6dc0518d94e9a009997b081a1ab] + +Backport Changes: +- Adjusted the upstream hunk to match the GnuTLS 3.8.12 code layout. +- Drop .gitignore from the backport. + +Reported-by: Doria Tang of Stony Brook University +Fixes: #1815 +Fixes: CVE-2026-5419 +Fixes: GNUTLS-SA-2026-04-29-13 +CVSS: 3.7 Low CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N +Signed-off-by: Daiki Ueno <[email protected]> +Signed-off-by: Jakub Szczudlo <[email protected]> + +--- + lib/crypto-api.c | 54 +++++++++++++++++------ + lib/libgnutls.map | 2 + + tests/Makefile.am | 2 +- + tests/pkcs7-pad.c | 109 ++++++++++++++++++++++++++++++++++++++++++++++ + 4 files changed, 153 insertions(+), 14 deletions(-) + create mode 100644 tests/pkcs7-pad.c + +diff --git a/lib/crypto-api.c b/lib/crypto-api.c +index 01539d5b52..32143e9de0 100644 +--- a/lib/crypto-api.c ++++ b/lib/crypto-api.c +@@ -498,6 +498,39 @@ error: + return ret; + } + ++/* If succeeds, returns the number of padding bytes to be removed; ++ * zero otherwise. ++ */ ++unsigned int _gnutls_pkcs7_unpad(const uint8_t *block, unsigned int block_size) ++{ ++ uint8_t padding = block[block_size - 1]; ++ volatile unsigned int mask = ~0; ++ volatile unsigned int count = 0; ++ ++ /* Count consecutive PADDING bytes from the end, in a ++ * constant-time manner. ++ */ ++ for (size_t i = block_size; i > 0; i--) { ++ volatile unsigned int mask2; ++ ++ mask2 = -(unsigned int)(block[i - 1] == padding); ++ mask2 &= -(unsigned int)(count < padding); ++ ++ /* MASK is initially ~0 and will be flipped to 0 upon first ++ * non-padding bytes. ++ */ ++ mask &= mask2; ++ count += 1 & mask; ++ } ++ ++ /* PADDING == 0 is effectively excluded here, given COUNT ++ * will never be 0. ++ */ ++ mask = -(unsigned int)(count <= block_size); ++ mask &= -(unsigned int)(count == padding); ++ return count & mask; ++} ++ + /** + * gnutls_cipher_decrypt3: + * @handle: is a #gnutls_cipher_hd_t type +@@ -532,22 +565,17 @@ int gnutls_cipher_decrypt3(gnutls_cipher_hd_t handle, const void *ctext, + if (_gnutls_cipher_type(h->ctx_enc.e) == CIPHER_BLOCK && + (flags & GNUTLS_CIPHER_PADDING_PKCS7)) { + uint8_t *p = ptext; +- uint8_t padding = p[*ptext_len - 1]; +- if (!padding || +- padding > _gnutls_cipher_get_block_size(h->ctx_enc.e)) { +- return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED); +- } +- /* Check that the prior bytes are all PADDING */ +- for (size_t i = *ptext_len - padding; i < *ptext_len; i++) { +- if (padding != p[*ptext_len - 1]) { +- return gnutls_assert_val( +- GNUTLS_E_DECRYPTION_FAILED); +- } +- } ++ size_t block_size = _gnutls_cipher_get_block_size(h->ctx_enc.e); ++ uint8_t *block = &p[*ptext_len - block_size]; ++ unsigned int padding = _gnutls_pkcs7_unpad(block, block_size); ++ volatile unsigned int mask; ++ ++ mask = -(unsigned int)(padding == 0); ++ ret = GNUTLS_E_DECRYPTION_FAILED & mask; + *ptext_len -= padding; + } + +- return 0; ++ return ret; + } + + /** +diff --git a/lib/libgnutls.map b/lib/libgnutls.map +index 955704e..5cc12c8 100644 +--- a/lib/libgnutls.map ++++ b/lib/libgnutls.map +@@ -1574,4 +1574,6 @@ GNUTLS_PRIVATE_3_4 { + _gnutls_pathbuf_append; + _gnutls_pathbuf_truncate; + _gnutls_pathbuf_deinit; ++ # needed by tests/pkcs7-pad ++ _gnutls_pkcs7_unpad; + } GNUTLS_3_4; +diff --git a/tests/Makefile.am b/tests/Makefile.am +index ab2685c..1304d2f 100644 +--- a/tests/Makefile.am ++++ b/tests/Makefile.am +@@ -241,7 +241,7 @@ ctests += mini-record-2 simple gnutls_hmac_fast set_pkcs12_cred cert certuniquei + x509cert-dntypes id-on-xmppAddr tls13-compat-mode ciphersuite-name \ + x509-upnconstraint xts-key-check cipher-padding pkcs7-verify-double-free \ + fips-rsa-sizes tls12-rehandshake-ticket pathbuf tls-force-ems \ +- psk-importer privkey-derive dh-compute2 ecdh-compute2 \ ++ psk-importer privkey-derive dh-compute2 ecdh-compute2 pkcs7-pad \ + mini-dtls-fragments + + ctests += tls-channel-binding +diff --git a/tests/pkcs7-pad.c b/tests/pkcs7-pad.c +new file mode 100644 +index 0000000..d4c3798 +--- /dev/null ++++ b/tests/pkcs7-pad.c +@@ -0,0 +1,109 @@ ++/* ++ * Copyright (C) 2026 Red Hat, Inc. ++ * ++ * This file is part of GnuTLS. ++ * ++ * GnuTLS is free software; you can redistribute it and/or modify it ++ * under the terms of the GNU General Public License as published by ++ * the Free Software Foundation; either version 3 of the License, or ++ * (at your option) any later version. ++ * ++ * GnuTLS is distributed in the hope that it will be useful, but ++ * WITHOUT ANY WARRANTY; without even the implied warranty of ++ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU ++ * General Public License for more details. ++ * ++ * You should have received a copy of the GNU General Public License ++ * along with GnuTLS. If not, see <https://www.gnu.org/licenses/>. ++ */ ++ ++/* Test that _gnutls_pkcs7_unpad is branch-free, using valgrind */ ++ ++#ifdef HAVE_CONFIG_H ++#include "config.h" ++#endif ++ ++#include <stdint.h> ++#include <string.h> ++ ++#ifdef HAVE_VALGRIND_MEMCHECK_H ++#include <valgrind/memcheck.h> ++#endif ++ ++#include "utils.h" ++ ++static inline void _gnutls_memory_mark_undefined(void *addr, size_t size) ++{ ++#ifdef HAVE_VALGRIND_MEMCHECK_H ++ if (RUNNING_ON_VALGRIND) ++ VALGRIND_MAKE_MEM_UNDEFINED(addr, size); ++#endif ++} ++ ++static inline void _gnutls_memory_mark_defined(void *addr, size_t size) ++{ ++#ifdef HAVE_VALGRIND_MEMCHECK_H ++ if (RUNNING_ON_VALGRIND) ++ VALGRIND_MAKE_MEM_DEFINED(addr, size); ++#endif ++} ++ ++extern unsigned int _gnutls_pkcs7_unpad(const uint8_t *block, ++ unsigned int block_size); ++ ++static unsigned int wrap_pkcs7_unpad(uint8_t *block, unsigned int block_size) ++{ ++ unsigned int padding; ++ ++ _gnutls_memory_mark_undefined(block, block_size); ++ ++ padding = _gnutls_pkcs7_unpad(block, block_size); ++ ++ _gnutls_memory_mark_defined(block, block_size); ++ _gnutls_memory_mark_defined(&padding, sizeof(padding)); ++ ++ return padding; ++} ++ ++#define PAD 5 ++ ++void doit(void) ++{ ++ uint8_t block[16]; ++ unsigned int padding; ++ ++ memset(block, 0xFF, sizeof(block)); ++ memset(&block[sizeof(block) - PAD], PAD, PAD); ++ ++ padding = wrap_pkcs7_unpad(block, sizeof(block)); ++ if (padding != PAD) ++ fail("padding should be %d\n", PAD); ++ ++ /* The last padding byte exceeds the block size */ ++ block[sizeof(block) - 1] = sizeof(block) + 1; ++ padding = wrap_pkcs7_unpad(block, sizeof(block)); ++ if (padding != 0) ++ fail("padding should be 0\n"); ++ block[sizeof(block) - 1] = PAD; ++ ++ /* The last padding byte is zero */ ++ block[sizeof(block) - 1] = 0; ++ padding = wrap_pkcs7_unpad(block, sizeof(block)); ++ if (padding != 0) ++ fail("padding should be 0\n"); ++ block[sizeof(block) - 1] = PAD; ++ ++ /* The first padding byte is invalid */ ++ block[sizeof(block) - PAD] = PAD + 1; ++ padding = wrap_pkcs7_unpad(block, sizeof(block)); ++ if (padding != 0) ++ fail("padding should be 0\n"); ++ block[sizeof(block) - PAD] = PAD; ++ ++ /* The byte before the first padding equals to PAD */ ++ block[sizeof(block) - PAD - 1] = PAD; ++ padding = wrap_pkcs7_unpad(block, sizeof(block)); ++ if (padding != PAD) ++ fail("padding should be %d\n", PAD); ++ block[sizeof(block) - PAD - 1] = 0xFF; ++} +-- +2.43.0 + diff --git a/meta/recipes-support/gnutls/gnutls_3.8.12.bb b/meta/recipes-support/gnutls/gnutls_3.8.12.bb index d513752072c..538fd9c9e0d 100644 --- a/meta/recipes-support/gnutls/gnutls_3.8.12.bb +++ b/meta/recipes-support/gnutls/gnutls_3.8.12.bb @@ -41,6 +41,7 @@ SRC_URI = "https://www.gnupg.org/ftp/gcrypt/gnutls/v${SHRT_VER}/gnutls-${PV}.tar file://CVE-2026-42011_p2.patch \ file://CVE-2026-42010.patch \ file://CVE-2026-33845.patch \ + file://CVE-2026-5419.patch \ " SRC_URI[sha256sum] = "a7b341421bfd459acf7a374ca4af3b9e06608dcd7bd792b2bf470bea012b8e51"
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