Samsung HEIF Decoder CVE-2026-21126

Exploitation requires local code execution on a Samsung mobile device - specifically an app or process able to feed a crafted HEIF file into the cover-image decoding path of libsimba.heifdec.media.samsung.so (AV:L). No authentication or user interaction is required once an attacker has local presence (PR:N/UI:N), so a co-resident unprivileged app is sufficient. The principal limiting factor is the local attack vector: the attacker must already have an app or foothold on the device, and exposure is bounded to builds prior to SMR Oct-2026 Release 1 - patched devices are not affected. Impact is confined to an out-of-bounds write (integrity), with no vendor-asserted confidentiality or availability effect.

This is a medium-severity local vulnerability (CVSS 4.0 base 6.9) in Samsung's HEIF image decoder library (libsimba.heifdec.media.samsung.so). The CVSS 4.0 vector (AV:L/AC:L/AT:N/PR:N/UI:N) indicates a local attack vector with low complexity, no privileges, and no user interaction, meaning any locally-installed, unprivileged application could trigger the flaw by supplying a crafted HEIF file for cover-image decoding. Impact is scoped narrowly to integrity (VI:H) with no confidentiality (VC:N) or availability (VA:N) impact in the vendor rating, consistent with an out-of-bounds write primitive rather than information disclosure or crash. No EPSS score, SSVC decision, KEV listing, or POC is present in the provided data, so there is no public exploit identified at time of analysis and no evidence of active exploitation; this reads as a priority patch for Samsung mobile fleets but not an emergency. A key caveat: AV:L plus PR:N/UI:N implies a co-resident malicious or compromised app is the realistic threat model, so real-world risk depends heavily on whether an attacker can get code onto the device first - the raw 6.9 overstates risk for a well-managed device and understates it where sideloaded apps are common. The isolated VI:H with no availability impact is slightly unusual for a memory-corruption bug; an OOB write typically also risks crashes, so the pure-integrity rating should be verified against the forthcoming Samsung advisory.

A malicious or compromised unprivileged app installed on a Samsung device supplies a specially crafted HEIF image and triggers cover-image decoding by libsimba.heifdec.media.samsung.so. Improper input validation causes an out-of-bounds memory write, which an attacker could leverage toward memory corruption in the media-processing context. No public exploit code is available at time of analysis.