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Out-of-bounds heap write in FFmpeg RASC decoder decode_dlta()

IdentifiersCVE-2026-58049CWE-787

CVE-2026-58049 is a high-severity memory corruption vulnerability in FFmpeg’s RASC video decoder, specifically the decode_dlta() function in libavcodec/rasc.c. The flaw arises because the decoder performs 32-bit reads and writes at the current row cursor before enforcing the NEXT_LINE row-boundary check, and because the DLTA region is validated in pixel units rather than byte units. On PAL8 frames, this mismatch can allow a DLTA run to access several bytes past the allocated row buffer. When libavcodec decodes a crafted media stream using the RASC FourCC, the attacker can trigger a bitstream-controlled out-of-bounds heap write together with an adjacent out-of-bounds read, resulting in heap memory corruption.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can cause heap memory corruption during media decoding. The reported effects include a bitstream-controlled out-of-bounds heap write and adjacent out-of-bounds read, which can compromise confidentiality, integrity, and availability of the decoding process. Depending on allocator state and surrounding memory layout, this may lead to process crash, abnormal decoder behavior, or potentially further exploitation of the affected process.

Mitigation

If you can’t patch tonight, do this now.

Until patched builds are deployed, avoid decoding untrusted or externally supplied media streams that use the RASC FourCC. Disable or exclude support for the vulnerable RASC decoder where operationally feasible, and isolate FFmpeg-based decoding in a sandboxed or least-privileged environment to reduce impact from malformed media input. Additional input validation or pre-screening of media files may reduce exposure but is not a substitute for patching.

Remediation

Patch, then assume compromise.

Update FFmpeg to a version containing the vendor fix for CVE-2026-58049. Apply upstream or downstream vendor patches addressing the bounds handling in the RASC decoder, particularly the decode_dlta() logic in libavcodec/rasc.c. If packaged builds are used, deploy the latest security-updated distribution package that includes the fix.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

FfmpegFfmpegapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

7 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

7 SOURCESView more in app

cvefeed high severityNews

Jun 28, 2026

CVE-2026-58049 - FFmpeg - Out-of-Bounds Write in RASC Decoder decode_dlta()

An out-of-bounds heap write and adjacent out-of-bounds read vulnerability in FFmpeg's RASC decoder (decode_dlta in libavcodec/rasc.c) that can be triggered by a crafted media stream, leading to memory corruption.

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Exposure mapping

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Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity6

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-58049

NVD

nvd.nist.gov/vuln/detail/CVE-2026-58049

MITRE CWE · CWE-787

cwe.mitre.org