CVE-2026-21091 is an out-of-bounds write in libcodec2secevrcdec.so, an audio decoder library on Samsung Android devices. The record scores it 7.8 (High) and says a local attacker can write out-of-bounds memory. Samsung lists the fix in SMR Sep-2026 Release 1.
What's affected
Samsung's September 2026 bulletin lists the libcodec2secevrcdec.so issue (SVE-2026-2066) as affecting Android 14, 15, 16 and 17 on Samsung devices, fixed in SMR Sep-2026 Release 1.
Source conflict to note: the record scores this 7.8 (High), while Samsung's bulletin rates it Moderate. Both are reported here.
Weakness class: CWE-787.
How to check if you're exposed
On a Samsung phone or tablet, open Settings, then About phone, then Software information, and read the Android security patch level. Samsung ships these fixes in the Samsung Mobile Security Maintenance Release (SMR) named in the bulletin, so a September 2026 patch level or later is the thing to look for. If you manage a fleet, your mobile device management console can report the patch level and Android version per device.
The bulletin lists Android 14, 15, 16 and 17 as affected, so any current Samsung device on those versions that has not taken the September 2026 SMR should be treated as exposed. Samsung does not publish a per-model table on the page, so check the update status on the device itself rather than assuming from the model name.
What to do now
- Install the September 2026 Samsung security update (SMR Sep-2026 Release 1) on every managed Samsung device. Carriers sometimes roll it out later than Samsung, so confirm on the device.
- Check whether any managed app on your devices plays or records audio in unusual formats. If so, include those devices in the first update wave.
- Report the patch level in your MDM inventory and set a compliance rule that flags devices more than one SMR behind.
- Keep the Samsung bulletin as your source of truth, and re-read it, because the vendor updated its vulnerability list after first publication.
Why it matters
The library name points to an EVRC audio codec decoder in Samsung's Codec2 media stack. Codecs take compressed input and turn it into raw audio, and a length or size miscalculation in that step can write past the end of a buffer (CWE-787). The vendor does not describe the trigger, so we describe only the class of weakness.
Codec libraries are a steady source of memory safety bugs across every platform, since they are old, performance sensitive and written in C or C plus plus. Platform vendors patch them in monthly bulletins, which is why staying current matters more than any single fix.
The attack vector in the record is local, with low complexity and low privileges required and no user interaction. That means the attacker needs code already running on the device, for example a malicious or compromised app. Local flaws still matter on phones, because the app sandbox is the main wall between one app and the rest of the device, and a bug in a system component can let one app reach beyond it.
The CISA Known Exploited Vulnerabilities flag is false in the record, and the Samsung bulletin we read does not describe exploitation. Treat this as a patch in the normal monthly cycle, not an emergency, but do not let it sit for months.
Quick check
Do I need to worry about phone calls?
The bulletin does not say how the decoder is reached, and we do not infer one. The record's attack vector is local.
Which Android versions are affected?
Samsung lists Android 14, 15, 16 and 17 for this bulletin.
Sources
Last reviewed: 18 October 2026.
