Backport the SFTP symlink bounds checking fix for CVE-2025-15661.
The initial fix requires the LIBSSH2_UNCONST compatibility backport on
libssh2 1.11.1. Also include the upstream follow-up fixing
SSH_FXP_STATUS handling introduced by the initial security fix.
The patches are based on the upstream fixes and Debian's libssh2 1.11.1
backports.
Signed-off-by: Stefan Müller <stefan.mueller@rey-technology.com>
---
Backport to: 2025.02.x
---
...-sftp-symlink-fix-out-of-bounds-read.patch | 116 ++++++++++++++++++
...ibssh2-priv-backport-LIBSSH2_UNCONST.patch | 29 +++++
...-symlink-fix-SSH_FXP_STATUS-response.patch | 46 +++++++
package/libssh2/libssh2.mk | 5 +
4 files changed, 196 insertions(+)
create mode 100644 package/libssh2/0004-sftp-symlink-fix-out-of-bounds-read.patch
create mode 100644 package/libssh2/0005-libssh2-priv-backport-LIBSSH2_UNCONST.patch
create mode 100644 package/libssh2/0006-sftp-symlink-fix-SSH_FXP_STATUS-response.patch
diff --git a/package/libssh2/0004-sftp-symlink-fix-out-of-bounds-read.patch b/package/libssh2/0004-sftp-symlink-fix-out-of-bounds-read.patch
new file mode 100644
index 0000000000..142dda81c9
--- /dev/null
+++ b/package/libssh2/0004-sftp-symlink-fix-out-of-bounds-read.patch
@@ -0,0 +1,116 @@
+From 2dae3024897e1898d389835151f4e9606227721d Mon Sep 17 00:00:00 2001
+From: Will Cosgrove <will@panic.com>
+Date: Fri, 10 Oct 2025 08:26:20 -0700
+Subject: [PATCH] Update sftp_symlink to avoid out of bounds read on malformed
+ packet #1705 (#1717)
+
+
+CVE: CVE-2025-15661
+Upstream:
https://github.com/libssh2/libssh2/commit/2dae3024897e1898d389835151f4e9606227721d
+Signed-off-by: Stefan Müller <stefan.mueller@rey-technology.com>
+---
+--- libssh2-1.11.1.orig/src/sftp.c
++++ libssh2-1.11.1/src/sftp.c
+@@ -3795,15 +3795,19 @@ static int sftp_symlink(LIBSSH2_SFTP *sf
+ {
+ LIBSSH2_CHANNEL *channel = sftp->channel;
+ LIBSSH2_SESSION *session = channel->session;
+- size_t data_len = 0, link_len;
++ size_t data_len = 0, lk_len;
+ /* 13 = packet_len(4) + packet_type(1) + request_id(4) + path_len(4) */
+ ssize_t packet_len =
+ path_len + 13 +
+ ((link_type == LIBSSH2_SFTP_SYMLINK) ? (4 + target_len) : 0);
+ unsigned char *s, *data = NULL;
++ struct string_buf buf;
+ static const unsigned char link_responses[2] =
+ { SSH_FXP_NAME, SSH_FXP_STATUS };
+ int retcode;
++ unsigned char packet_type;
++ uint32_t tmp_u32;
++ unsigned char *lk_target;
+
+ if(sftp->symlink_state == libssh2_NB_state_idle) {
+ sftp->last_errno = LIBSSH2_FX_OK;
+@@ -3891,8 +3895,25 @@ static int sftp_symlink(LIBSSH2_SFTP *sf
+
+ sftp->symlink_state = libssh2_NB_state_idle;
+
+- if(data[0] == SSH_FXP_STATUS) {
+- retcode = _libssh2_ntohu32(data + 5);
++ buf.data = (unsigned char *)LIBSSH2_UNCONST(data);
++ buf.dataptr = buf.data;
++ buf.len = data_len;
++
++ if(_libssh2_get_byte(&buf, &packet_type)) {
++ LIBSSH2_FREE(session, data);
++ return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
++ "SFTP Protocol Error (type)");
++ }
++
++ if(packet_type == SSH_FXP_STATUS) {
++ if(_libssh2_get_u32(&buf, &tmp_u32)) {
++ LIBSSH2_FREE(session, data);
++ return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
++ "SFTP Protocol Error (code)");
++ }
++
++ retcode = (int)tmp_u32;
++
+ LIBSSH2_FREE(session, data);
+ if(retcode == LIBSSH2_FX_OK)
+ return LIBSSH2_ERROR_NONE;
+@@ -3903,30 +3924,37 @@ static int sftp_symlink(LIBSSH2_SFTP *sf
+ }
+ }
+
+- if(_libssh2_ntohu32(data + 5) < 1) {
++ /* advance past id */
++ if(_libssh2_get_u32(&buf, &tmp_u32)) {
+ LIBSSH2_FREE(session, data);
+ return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
+- "Invalid READLINK/REALPATH response, "
+- "no name entries");
++ "SFTP Protocol Error (id)");
+ }
+
+- if(data_len < 13) {
+- if(data_len > 0) {
+- LIBSSH2_FREE(session, data);
+- }
++ /* look for at least one link */
++ if(_libssh2_get_u32(&buf, &tmp_u32) || tmp_u32 < 1) {
++ LIBSSH2_FREE(session, data);
+ return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
+- "SFTP stat packet too short");
++ "Invalid READLINK/REALPATH response, "
++ "no name entries");
+ }
+
+- /* this reads a u32 and stores it into a signed 32bit value */
+- link_len = _libssh2_ntohu32(data + 9);
+- if(link_len < target_len) {
+- memcpy(target, data + 13, link_len);
+- target[link_len] = 0;
+- retcode = (int)link_len;
++ if(_libssh2_get_string(&buf, &lk_target, &lk_len) == LIBSSH2_ERROR_NONE) {
++ if(lk_len < target_len) {
++ memcpy(target, lk_target, lk_len);
++ target[lk_len] = '\0';
++ retcode = (int)lk_len;
++ }
++ else {
++ retcode = LIBSSH2_ERROR_BUFFER_TOO_SMALL;
++ }
+ }
+- else
+- retcode = LIBSSH2_ERROR_BUFFER_TOO_SMALL;
++ else {
++ LIBSSH2_FREE(session, data);
++ return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
++ "SFTP Protocol Error (filename)");
++ }
++
+ LIBSSH2_FREE(session, data);
+
+ return retcode;
diff --git a/package/libssh2/0005-libssh2-priv-backport-LIBSSH2_UNCONST.patch b/package/libssh2/0005-libssh2-priv-backport-LIBSSH2_UNCONST.patch
new file mode 100644
index 0000000000..34ad92409c
--- /dev/null
+++ b/package/libssh2/0005-libssh2-priv-backport-LIBSSH2_UNCONST.patch
@@ -0,0 +1,29 @@
+Needed by the fix for CVE-2025-15661
+
+Cherrypicked from
+commit 606c102e52f8447de2b745dd6c5ddf418defc519
+Author: Viktor Szakats <commit@vsz.me>
+Date: Thu Jan 30 21:18:23 2025 +0100
+
+
+CVE: CVE-2025-15661
+Upstream:
https://github.com/libssh2/libssh2/commit/606c102e52f8447de2b745dd6c5ddf418defc519
+Signed-off-by: Stefan Müller <stefan.mueller@rey-technology.com>
+---
+--- libssh2-1.11.1.orig/src/libssh2_priv.h
++++ libssh2-1.11.1/src/libssh2_priv.h
+@@ -117,6 +117,14 @@
+ #define UINT32_MAX 0xffffffffU
+ #endif
+
++#ifdef _WIN64
++#define LIBSSH2_UNCONST(p) ((void *)(libssh2_uint64_t)(const void *)(p))
++#elif defined(_MSC_VER)
++#define LIBSSH2_UNCONST(p) ((void *)(unsigned int)(const void *)(p))
++#else
++#define LIBSSH2_UNCONST(p) ((void *)(uintptr_t)(const void *)(p))
++#endif
++
+ #if (defined(__GNUC__) || defined(__clang__)) && \
+ defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L) && \
+ !defined(LIBSSH2_NO_FMT_CHECKS)
diff --git a/package/libssh2/0006-sftp-symlink-fix-SSH_FXP_STATUS-response.patch b/package/libssh2/0006-sftp-symlink-fix-SSH_FXP_STATUS-response.patch
new file mode 100644
index 0000000000..2883c102dc
--- /dev/null
+++ b/package/libssh2/0006-sftp-symlink-fix-SSH_FXP_STATUS-response.patch
@@ -0,0 +1,46 @@
+From 4ed26f5740bdd409269ed9fb48a28bf8f565b681 Mon Sep 17 00:00:00 2001
+From: Will Cosgrove <will@panic.com>
+Date: Mon, 20 Oct 2025 14:04:52 -0700
+Subject: [PATCH] Fix sftp_symlink when getting SSH_FXP_STATUS response (#1731)
+
+Move advancing past packet ID before reading the FXP_STATUS response.
+
+CVE: CVE-2025-15661
+Upstream:
https://github.com/libssh2/libssh2/commit/4ed26f5740bdd409269ed9fb48a28bf8f565b681
+Signed-off-by: Stefan Müller <stefan.mueller@rey-technology.com>
+---
+ src/sftp.c | 14 +++++++-------
+ 1 file changed, 7 insertions(+), 7 deletions(-)
+
+diff --git a/src/sftp.c b/src/sftp.c
+index 70d7686daf..bb297b831a 100644
+--- a/src/sftp.c
++++ b/src/sftp.c
+@@ -4006,6 +4006,13 @@ static int sftp_symlink(LIBSSH2_SFTP *sftp, const char *path,
+ "SFTP Protocol Error (type)");
+ }
+
++ /* advance past id */
++ if(_libssh2_get_u32(&buf, &tmp_u32)) {
++ LIBSSH2_FREE(session, data);
++ return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
++ "SFTP Protocol Error (id)");
++ }
++
+ if(packet_type == SSH_FXP_STATUS) {
+ if(_libssh2_get_u32(&buf, &tmp_u32)) {
+ LIBSSH2_FREE(session, data);
+@@ -4025,13 +4032,6 @@ static int sftp_symlink(LIBSSH2_SFTP *sftp, const char *path,
+ }
+ }
+
+- /* advance past id */
+- if(_libssh2_get_u32(&buf, &tmp_u32)) {
+- LIBSSH2_FREE(session, data);
+- return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
+- "SFTP Protocol Error (id)");
+- }
+-
+ /* look for at least one link */
+ if(_libssh2_get_u32(&buf, &tmp_u32) || tmp_u32 < 1) {
+ LIBSSH2_FREE(session, data);
diff --git a/package/libssh2/libssh2.mk b/package/libssh2/libssh2.mk
index 0ccf5effb3..6b2d774b38 100644
--- a/package/libssh2/libssh2.mk
+++ b/package/libssh2/libssh2.mk
@@ -22,6 +22,11 @@ LIBSSH2_IGNORE_CVES += CVE-2026-55199
# 0003-transport-c-Additional-boundary-checks-for-packet-length.patch
LIBSSH2_IGNORE_CVES += CVE-2026-55200
+# 0004-sftp-symlink-fix-out-of-bounds-read.patch
+# 0005-libssh2-priv-backport-LIBSSH2_UNCONST.patch
+# 0006-sftp-symlink-fix-SSH_FXP_STATUS-response.patch
+LIBSSH2_IGNORE_CVES += CVE-2025-15661
+
ifeq ($(BR2_PACKAGE_LIBSSH2_MBEDTLS),y)
LIBSSH2_DEPENDENCIES += mbedtls
LIBSSH2_CONF_OPTS += --with-libmbedcrypto-prefix=$(STAGING_DIR)/usr \
--
2.25.1
