Submitted By: Joe Locash Date: 2026-05-03 Initial Package Version: 1.22.2 Upstream Status: Applied Origin: Upstream commit acea618 in the 1.22 branch Description: Fixes CVE-2026-40355 and CVE-2026-40356 From acea6182e46fff3d1d64a3172cdff307b07ca441 Mon Sep 17 00:00:00 2001 From: Greg Hudson Date: Wed, 8 Apr 2026 17:57:59 -0400 Subject: [PATCH] Fix two NegoEx parsing vulnerabilities In parse_nego_message(), check the result of the second call to vector_base() before dereferencing it. In parse_message(), check for a short header_len to prevent an integer underflow when calculating the remaining message length. Reported by Cem Onat Karagun. CVE-2026-40355: In MIT krb5 release 1.18 and later, if an application calls gss_accept_sec_context() on a system with a NegoEx mechanism registered in /etc/gss/mech, an unauthenticated remote attacker can trigger a null pointer dereference, causing the process to terminate. CVE-2026-40356: In MIT krb5 release 1.18 and later, if an application calls gss_accept_sec_context() on a system with a NegoEx mechanism registered in /etc/gss/mech, an unauthenticated remote attacker can trigger a read overrun of up to 52 bytes, possibly causing the process to terminate. Exfiltration of the bytes read does not appear possible. (cherry picked from commit 2e75f0d9362fb979f5fc92829431a590a130929f) ticket: 9205 version_fixed: 1.22.3 --- src/lib/gssapi/spnego/negoex_util.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/src/lib/gssapi/spnego/negoex_util.c b/src/lib/gssapi/spnego/negoex_util.c index edc5462e844..a65238e5730 100644 --- a/src/lib/gssapi/spnego/negoex_util.c +++ b/src/lib/gssapi/spnego/negoex_util.c @@ -253,6 +253,10 @@ parse_nego_message(OM_uint32 *minor, struct k5input *in, offset = k5_input_get_uint32_le(in); count = k5_input_get_uint16_le(in); p = vector_base(offset, count, EXTENSION_LENGTH, msg_base, msg_len); + if (p == NULL) { + *minor = ERR_NEGOEX_INVALID_MESSAGE_SIZE; + return GSS_S_DEFECTIVE_TOKEN; + } for (i = 0; i < count; i++) { extension_type = load_32_le(p + i * EXTENSION_LENGTH); if (extension_type & EXTENSION_FLAG_CRITICAL) { @@ -391,7 +395,8 @@ parse_message(OM_uint32 *minor, spnego_gss_ctx_id_t ctx, struct k5input *in, msg_len = k5_input_get_uint32_le(in); conv_id = k5_input_get_bytes(in, GUID_LENGTH); - if (in->status || msg_len > token_remaining || header_len > msg_len) { + if (in->status || msg_len > token_remaining || + header_len < (size_t)(in->ptr - msg_base) || header_len > msg_len) { *minor = ERR_NEGOEX_INVALID_MESSAGE_SIZE; return GSS_S_DEFECTIVE_TOKEN; }