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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1779371809; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YIwiZmnjUXUCbjuzvEwbbIdtcVmXNfGuVljF3AGGI/k=; b=dDFIE12xmPELBZXNMGGYE2hUBBZTUtionowUftXUP8QPKs6M6SW8IupSwUjyaev2UvAeDi mG2Wlh9BfBdiqgXa1Z7xIDh+1XFvecug+l78tzUPT1enbohxxi9d59ye3uHyXSMzxCoHbR 6Qs9jGaihchk6H7eQ7jxJ3DmPkGgQfQ= X-MC-Unique: ojfDwKoeM-GD0ZiHJSEbtA-1 X-Mimecast-MFC-AGG-ID: ojfDwKoeM-GD0ZiHJSEbtA_1779371804 From: marcandre.lureau@redhat.com To: qemu-devel@nongnu.org Cc: stefanha@gmail.com, Heechan Kang , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= Subject: [PULL v2 08/38] ui: fix validation of VNC extended clipboard data length Date: Thu, 21 May 2026 17:55:19 +0400 Message-ID: <20260521135551.1752945-9-marcandre.lureau@redhat.com> In-Reply-To: <20260521135551.1752945-1-marcandre.lureau@redhat.com> References: <20260521135551.1752945-1-marcandre.lureau@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists1p.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=marcandre.lureau@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 8 X-Spam_score: 0.8 X-Spam_bar: / X-Spam_report: (0.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1779371937114158500 From: Heechan Kang QEMU's VNC extended clipboard handler inflates a client-controlled compressed clipboard payload. The code checks the declared text size against the total inflated buffer size: if (tsize < size) but then copies from: tbuf =3D buf + 4; qemu_clipboard_set_data(..., tsize, tbuf, true); The correct bound is the remaining data length after the 4-byte length field, not the total inflated buffer length. As a result, a VNC client can make QEMU copy up to 3 bytes past the end of the inflated heap buffer. With a second VNC client, those copied bytes are observable through the normal VNC extended clipboard PROVIDE path. Fixes: CVE-2026-8343 Reported-by: Heechan Kang Reported-by: Feifan Qian Reviewed-by: Daniel P. Berrang=C3=A9 Signed-off-by: Heechan Kang [DB: added #include and 'return' statements] Signed-off-by: Daniel P. Berrang=C3=A9 Reviewed-by: Marc-Andr=C3=A9 Lureau Message-ID: <20260512095543.459949-1-berrange@redhat.com> --- ui/vnc-clipboard.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/ui/vnc-clipboard.c b/ui/vnc-clipboard.c index 124b6fbd9c2..fa05d86f424 100644 --- a/ui/vnc-clipboard.c +++ b/ui/vnc-clipboard.c @@ -23,6 +23,7 @@ */ =20 #include "qemu/osdep.h" +#include "qemu/error-report.h" #include "vnc.h" #include "vnc-jobs.h" =20 @@ -282,10 +283,16 @@ void vnc_client_cut_text_ext(VncState *vs, int32_t le= n, uint32_t flags, uint8_t buf && size >=3D 4) { uint32_t tsize =3D read_u32(buf, 0); uint8_t *tbuf =3D buf + 4; - if (tsize < size) { + if (tsize <=3D size - 4) { qemu_clipboard_set_data(&vs->cbpeer, vs->cbinfo, QEMU_CLIPBOARD_TYPE_TEXT, tsize, tbuf, true); + } else { + error_report("vnc: malformed extended clipboard payload " + "with text length %u exceeding available %u", + tsize, size - 4); + vnc_client_error(vs); + return; } } } --=20 2.54.0