CVE-2026-127915mcu-tools mcuboot out-of-bounds read
CVE-2026-127915 is a out-of-bounds read in mcu-tools mcuboot, rated low (2.0 on CVSS 3.1).
Why this priority: Low severity, with no exploitation signal.
Published · Updated · NVD status: Received
What it is
Code reads past the end of a buffer, leaking memory contents or crashing.
How it is reached
An attacker can exploit it with physical access to the device, without an account, and nobody has to click anything. Success also depends on conditions the attacker does not fully control.
What an attacker gains
The direct impact is limited: partial access to data or a partial outage. In practice, this kind of flaw lets an attacker crash the process, read memory, or in the worst case run code.
Is it being exploited?
There is no public report of exploitation yet.
What to do
- Upgrade mcu-tools mcuboot to 2.5.0 or later.
Description from NVD
The MCUboot TLV iterator bootutil_tlv_iter_next() in boot/bootutil/src/tlv.c walks image trailer TLVs with a single loop guard (it->tlv_off < it->tlv_end) and advances by sizeof(struct image_tlv) + tlv.it_len using the attacker-controlled it_len field, without validating that the entry's header or payload stays within it->tlv_end. As a result the 4-byte header read can extend up to 3 bytes past the declared TLV area, and the returned (off, len) can describe a payload that runs past it.
The path is pre-authentication: TLVs are parsed during bootutil_img_validate() before the signature is verified, and a crafted image can be presented through DFU / serial-recovery / OTA. However the impact is contained by surrounding guards: bootutil_img_validate() first rejects a TLV area larger than bootutil_max_image_size(), the default LOAD_IMAGE_DATA sink is flash_area_read() which bounds-checks against the flash partition and fails an out-of-partition read, and every payload consumer (EXPECTED_HASH_TLV, EXPECTED_KEY_TLV, EXPECTED_SIG_TLV, IMAGE_TLV_SEC_CNT) clamps len against a fixed buffer before copying.
The residual effect in a default flash build is therefore an out-of-region read confined to the attacker's own slot partition whose result is never observable, yielding at worst a clean validation failure rather than memory corruption or information disclosure. A genuine (though still bounded) out-of-bounds read remains under the non-default MCUBOOT_RAM_LOAD configuration, where LOAD_IMAGE_DATA is an unchecked memcpy. The fix is to validate each entry's header and payload against it->tlv_end inside the iterator.
What this means for your architecture.
A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.
Components it touches
- Native code: operating systems, browsers and firmware. The flaw sits wherever native code reads untrusted data.
- Network appliances and media or file parsers. The flaw sits wherever native code reads untrusted data.
Trust boundaries in play
- Host boundary. The attacker needs a foothold on the machine first; the flaw turns a small foothold into a bigger one.
- Wherever native code reads untrusted data. An attacker who crosses it can crash the process, read memory, or in the worst case run code.
Questions to answer about your own systems
- Where does mcu-tools mcuboot run in your systems, and at which version?
- Which of those devices sit where outsiders can touch them?
- What can it reach once compromised: which data stores, secrets and services?
Sources
- CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
- Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
- Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
- Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.