Amazon Linux 2 : qemu, --advisory ALAS2-2026-3866 (ALAS-2026-3866)

medium Nessus Plugin ID 337242

Synopsis

The remote Amazon Linux 2 host is missing a security update.

Description

The version of qemu installed on the remote host is prior to 3.1.0-8. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2-2026-3866 advisory.

In QEMU's VNC server implementation (ui/vnc.c), the set_pixel_format() function does not properly validate the red_max, green_max, and blue_max fields from a client'sSetPixelFormat message. These fields are received as 16-bit values but are stored internally as uint8_t. A malicious VNC client can send a max value above 255 (e.g., 0x0100) whichpasses the existing non-zero validation check but silently truncates to 0 upon assignment, leading to a division by zero in the Tight PNG palette encoding path. This allows a remoteattacker to crash the QEMU process, resulting in a denial of service for all guests served by that QEMU instance. Fixed in QEMU v11.0.3 and v10.0.12. (CVE-2026-15578)

In QEMU's USB redirection (usbredir) implementation, a use-after-free vulnerability exists in the usbredir_buffered_bulk_packet() function in hw/usb/redirect.c. When processing amulti-fragment buffered bulk packet that is split into max-packet-size chunks, only the final fragment owns the shared parser memory allocation (via free_on_destroy). If bufp_alloc()drops the final fragment due to queue overflow, it frees the backing buffer while earlier fragments already queued still hold interior pointers into it.
Subsequent guest bulk-INtransfers then read from freed heap memory. A malicious or compromised USB device (or a crafted usbredir stream) could trigger this condition, potentially leading to informationdisclosure from heap memory or a QEMU process crash (denial of service). This vulnerability has existed since QEMU v1.4.0-rc0 and is fixed in v11.0.3 and v10.0.12. (CVE-2026-15705)

Incorrect calculation of the boundary condition when tracking lossy rectangles in the worker thread will result in an OOB write which can corrupt further worker state, and/or trigger any guard pages that may lie beyond the VncWorker struct. This can be triggered through careful choice of the display resolution in the guest OS by an unprivileged user. (CVE-2026-48002)

Incorrect loop bounds in vnc_update_freq result in iterating past the last row and past the last column in the VNC stats array. With suitably chosen dimensions this could be a OOB read that accesses memory beyond the VncDisplay struct that the stats array is embedded in.

Should this hit a guard page, it could trigger a guest crash. If it does not, then the VNC frequency stats will be updated with garbage. (CVE-2026-48003)

In QEMU's VNC server implementation (ui/vnc.c), the vnc_refresh_lossy_rect() function contains an out-of- bounds write vulnerability when marking dirty bitmap rows during lossy tilerefresh. The function unconditionally marks a full VNC_STAT_RECT (64) rows of the dirty bitmap for each tile. When the display height is not a multiple of 64 pixels, the last tilerow is a partial tile and the loop writes past the end of the vs->dirty[VNC_MAX_HEIGHT] array. For example, with a 2160-pixel-high display, the last stat tile starts at y=2112 andthe 64-row loop writes rows 2112-2175, overflowing 16 rows (640 bytes) past the dirty bitmap into subsequent VncState fields. This heap buffer overflow could potentially be exploitedby a malicious VNC client that negotiates a specific display resolution to corrupt QEMU process memory, leading to denial of service or possibly arbitrary code execution. Fixed inQEMU v11.0.3 and v10.0.12.
(CVE-2026-61475)

In QEMU's USB redirection (usbredir) implementation (hw/usb/redirect.c), a malicious usbredir peer can send an ep_info message that resets max_packet_size to 0 after bulk receivinghas already started. This leads to multiple exploitable conditions: (1) an infinite loop in usbredir_buffered_bulk_packet() where the splitting loop increments by max_packet_size (0) and never progresses, (2) a SIGFPE (floating point exception) in usbredir_buffered_bulk_in_complete_ftdi() from a modulo-by-zero operation, and (3) a SIGFPE in usbredir_handle_buffered_bulk_in_data() from a division-by-zero when computing bytes_per_transfer. A malicious USB redirection peer can exploit this to crash the QEMU process (denial of service) orcause it to hang indefinitely. Fixed in QEMU v11.0.3 and v10.0.12. (CVE-2026-63319)

In QEMU's 9pfs (virtio-9p) implementation, the TXATTRCREATE and TXATTRWALK request handlers do not limit the number of simultaneously open xattr FIDs. Each xattr FID allocates ahost memory buffer for the extended attribute value. A malicious privileged guest user with direct 9p server access can exploit this by repeatedly creating xattr FIDs without closingthem, leading to unbounded host memory consumption and eventual host memory exhaustion (denial of service). This vulnerability has existed since QEMU v0.14.0-rc0 and is fixed inv11.0.3 and v10.0.12. (CVE-2026-8348)

An out-of-bounds heap read and integer underflow in the TCP urgent data handling (sosendoob) in freedesktop.org libslirp version before v4.9.2 on hypervisor host environments (e.g., QEMU) allows a privileged guest VM attacker (root or CAP_NET_RAW) to leak gigabytes of sensitive host-process heap memory via sending crafted TCP segments with manipulated URG flags and urgent pointers (ti_urp). (CVE-2026-9539)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Solution

Run 'yum update qemu' or or 'yum update --advisory ALAS2-2026-3866' to update your system.

Plugin Details

Severity: Medium

ID: 337242

File Name: al2_ALAS-2026-3866.nasl

Version: 1.1

Type: Local

Agent: unix

Family: Amazon Linux Local Security Checks

Published: 8/18/2026

Updated: 8/18/2026

Supported Sensors: Frictionless Assessment AWS, Frictionless Assessment Agent, Nessus Agent, Agentless Assessment, Continuous Assessment, Tenable Cloud Security, Tenable Self-Hosted Container Security, Nessus

Risk Information

VPR

Risk Factor: Low

Score: 3.3

Percentile: 50.91

CVSS v2

Risk Factor: Medium

Base Score: 4.6

Temporal Score: 3.4

Vector: CVSS2#AV:L/AC:L/Au:S/C:C/I:N/A:N

CVSS Score Source: CVE-2026-9539

CVSS v3

Risk Factor: Medium

Base Score: 6.5

Temporal Score: 5.7

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

CPE: cpe:/o:amazon:linux:2, p-cpe:/a:amazon:linux:ivshmem-tools, p-cpe:/a:amazon:linux:qemu-audio-alsa, p-cpe:/a:amazon:linux:qemu-audio-oss, p-cpe:/a:amazon:linux:qemu-audio-pa, p-cpe:/a:amazon:linux:qemu-audio-sdl, p-cpe:/a:amazon:linux:qemu-block-curl, p-cpe:/a:amazon:linux:qemu-block-dmg, p-cpe:/a:amazon:linux:qemu-block-iscsi, p-cpe:/a:amazon:linux:qemu-block-nfs, p-cpe:/a:amazon:linux:qemu-block-rbd, p-cpe:/a:amazon:linux:qemu-block-ssh, p-cpe:/a:amazon:linux:qemu-common, p-cpe:/a:amazon:linux:qemu-debuginfo, p-cpe:/a:amazon:linux:qemu-guest-agent, p-cpe:/a:amazon:linux:qemu-img, p-cpe:/a:amazon:linux:qemu-kvm-core, p-cpe:/a:amazon:linux:qemu-kvm, p-cpe:/a:amazon:linux:qemu-system-aarch64-core, p-cpe:/a:amazon:linux:qemu-system-aarch64, p-cpe:/a:amazon:linux:qemu-system-x86-core, p-cpe:/a:amazon:linux:qemu-system-x86, p-cpe:/a:amazon:linux:qemu-ui-curses, p-cpe:/a:amazon:linux:qemu-ui-gtk, p-cpe:/a:amazon:linux:qemu-ui-sdl, p-cpe:/a:amazon:linux:qemu-user-binfmt, p-cpe:/a:amazon:linux:qemu-user-static, p-cpe:/a:amazon:linux:qemu-user, p-cpe:/a:amazon:linux:qemu

Required KB Items: Host/local_checks_enabled, Host/AmazonLinux/release, Host/AmazonLinux/rpm-list

Exploit Ease: No known exploits are available

Patch Publication Date: 8/17/2026

Vulnerability Publication Date: 6/24/2026

Reference Information

CVE: CVE-2026-15578, CVE-2026-15705, CVE-2026-48002, CVE-2026-48003, CVE-2026-61475, CVE-2026-63319, CVE-2026-8348, CVE-2026-9539

Detections

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