Azure Sphere Information Disclosure Vulnerability
Description
Azure Sphere Information Disclosure Vulnerability
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
An information disclosure vulnerability in Azure Sphere's Littlefs filesystem allows uninitialized memory read via crafted syscalls, potentially leaking sensitive data.
Vulnerability
CVE-2020-16985 is an information disclosure vulnerability in the Littlefs filesystem functionality of Microsoft Azure Sphere 20.06. The vulnerability is a use of uninitialized resource (CWE-908) that occurs when a specially crafted set of syscalls triggers an uninitialized read. This issue affects applications that use mutable storage (as defined in the app manifest with MutableStorage capability); applications using only read-only storage are not vulnerable. The confirmed vulnerable version is Azure Sphere 20.06.
Exploitation
An attacker with local access to the Azure Sphere device can exploit this vulnerability by sending a sequence of specially crafted syscalls to the Littlefs filesystem. No authentication or user interaction is required (CVSS:3.0/AV:L/AC:L/PR:N/UI:N). The attacker must be able to execute syscalls on the target device, which is possible for any application running on the high-level core that has mutable storage enabled.
Impact
Successful exploitation results in an uninitialized memory read, leading to the disclosure of sensitive information from the kernel or other processes. The confidentiality impact is high, while integrity and availability are not affected. The scope of the compromise changes (S:C), meaning the leaked information may originate from a different security context than the attacker's application.
Mitigation
Microsoft has not publicly disclosed specific mitigation details in the available reference [1]. Users should ensure their Azure Sphere devices are updated to the latest OS version, as Microsoft typically addresses vulnerabilities through Azure Sphere OS updates. No workaround is available for applications that require mutable storage.
AI Insight generated on May 26, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.
Affected products
2cpe:2.3:a:microsoft:azure_sphere:*:*:*:*:*:*:*:*+ 1 more
- cpe:2.3:a:microsoft:azure_sphere:*:*:*:*:*:*:*:*range: 20.00
- (no CPE)
Patches
0No patches discovered yet.
Vulnerability mechanics
Root cause
"The Littlefs filesystem driver does not zero-fill newly allocated pages when a file is extended via truncate, causing stale cached page data to be returned to userspace on read."
Attack vector
An attacker with the ability to execute arbitrary code within an Azure Sphere high-level application that has `MutableStorage` enabled can trigger this vulnerability. The attacker opens a file in the mutable storage area (`/mnt/config/
Affected code
The vulnerability resides in the Linux kernel's `do_generic_file_read` function within the file `mm/filemap.c`, specifically in the interaction between the page cache and the Littlefs filesystem driver. When a file is truncated (via `truncate` syscall) to extend its size, the newly allocated pages are not zeroed before being returned to userspace. The kernel's `copy_page_to_iter` function copies a cached page that has the `PG_uptodate` flag set (0x8) but contains stale data from prior allocations, as demonstrated by the researcher's debugger output showing `page->flags = 8` [ref_id=1].
What the fix does
The advisory does not include a patch diff, but the root cause is that the Littlefs filesystem driver does not properly zero-fill pages when a file is extended via `truncate`. The kernel's generic file read path (`do_generic_file_read`) finds a cached page with `PG_uptodate` set and copies it to userspace without ensuring the page has been zeroed for the newly extended region. The fix would require the Littlefs driver to either invalidate cached pages on truncate or explicitly zero the extended portion of the file before marking pages as up-to-date [ref_id=1].
Preconditions
- configThe target application must have MutableStorage enabled in its app_manifest.json (SizeKB > 0)
- authAttacker must be able to execute arbitrary code within the Azure Sphere high-level application context
- networkAttacker must have local access to the device (AV:L per CVSS)
- inputAttacker must be able to call open(), write(), truncate(), and read() syscalls on files in the mutable storage partition
Generated on May 26, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.
References
2- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-16985mitrex_refsource_MISC
- www.talosintelligence.com/vulnerability_reports/TALOS-2020-1130mitrex_refsource_MISC
News mentions
0No linked articles in our index yet.