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The FFmpeg advisory for CVE-2026-58049 describes a memory-safety flaw in the RASC screen-capture decoder: while parsing a DLTA chunk, 32-bit reads or writes may cross a row boundary before the decoder checks that boundary. The advisory rates it CVSS v4 8.8 and says a crafted RASC stream can cause out-of-bounds access and memory corruption. It does not identify affected or patched versions, so a fixed release cannot be confirmed from the available information.
What is the FFmpeg bug?
The issue is in decode_dlta, the function that decodes DLTA data in FFmpeg’s RASC decoder. The GitHub Advisory Database entry for CVE-2026-58049 describes a parsing-boundary problem: some 32-bit operations can happen at the current row cursor before the decoder verifies that the cursor remains within the next-row boundary. The advisory also says the DLTA region is validated in pixel units rather than byte units.
In practical terms, the decoder’s bounds check may not account correctly for the width of an operation that reads or writes multiple bytes. The advisory says a specially crafted RASC media stream can trigger out-of-bounds access and memory corruption. That is the advisory’s account of the flaw; the source code provides context for how the decoder processes DLTA data but does not by itself demonstrate a working exploit.
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RASC DLTA data is handled as a sequence of runs. The FFmpeg implementation initializes cursor coordinates and row pointers, then processes different run types. In several branches, the code reads or writes 32-bit values through pointers based on the row buffers and the cursor position.
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The FFmpeg RASC decoder source includes a NEXT_LINE macro for row transitions and a dlta_room helper that checks whether cx + need <= w * bpp. The advisory’s concern is that a 32-bit operation can occur before the next-row boundary check, while region validation uses pixels rather than bytes. That combination can leave a mismatch between the logical pixel boundary and the number of bytes an operation touches.
This code context helps explain the reported risk, but it should not be mistaken for independent proof that a particular input overwrites a specific object or control-flow value.
What is known about severity and exploitability?
The advisory assigns CVE-2026-58049 a CVSS v4 base score of 8.8 and classifies it as CWE-787, an out-of-bounds write. Another secondary result displays 8.6, but does not explain the difference in scoring. The explicit score to cite from the advisory is 8.8 under CVSS v4; scores from different CVSS versions should not be treated as directly interchangeable.
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A Feedly search result repeats the title “I Fixed a Bug That Lived in FFmpeg for 8 Years” and describes an alleged PAL8 proof of concept involving a 64-by-1 frame and an adjacent callback-pointer overwrite. That is a secondary aggregation result, not the original technical write-up or an independent validation. The advisory and source cited here do not establish those exploit details, so they should be treated as unverified rather than as confirmed behavior.
Does “lived in FFmpeg for 8 years” describe a verified timeline?
The eight-year duration appears in the title reproduced by the secondary search result, but the available primary sources do not establish when the defect was introduced or how long it was present. The advisory entry says it was published June 28, 2026 and updated August 7, 2026; those are advisory dates, not the bug’s discovery or introduction dates. Without the original author’s supporting timeline or an identified introducing commit, “eight years” remains a title-level claim.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Which FFmpeg versions are affected or fixed?
The advisory lists both affected versions and patched versions as unknown. The current source page is not enough to infer a fix, and the sources cited here do not identify an upstream fix commit or fixed FFmpeg release. Do not assume that a particular version is safe or vulnerable based only on this advisory entry.
For deployments that use FFmpeg to process media from untrusted sources, check the advisory and the package provider’s security notices for the specific build in use. Distributors can backport fixes without changing to the upstream release number that a reader might expect, so verify the package’s own status rather than relying on a version comparison alone.
Quick Recap
What does the evidence establish?
| Evidence | What it supports | What it does not establish |
|---|---|---|
| GitHub Advisory Database, CVE-2026-58049 | The affected component is decode_dlta in the RASC decoder; it describes the row-boundary and pixel-versus-byte validation issue, out-of-bounds access and memory corruption, CVSS v4 8.8, and CWE-787. |
A fixed version, affected version range, or independently reproduced exploit. |
| FFmpeg RASC decoder source | The implementation has DLTA run branches with 32-bit reads or writes, row-transition handling through NEXT_LINE, and the dlta_room helper. |
That a specific crafted file achieves the exploit outcome described in a secondary report. |
| Feedly search result | A secondary report repeats the eight-year title and describes an alleged PAL8 proof of concept. | The original article’s evidence or independent confirmation of the proof-of-concept details. |
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