What is the ACE file format?
.ace files are associated with WinAce, a proprietary data archiving tool developed by e-merge GmbH. WinAce uses its own LZ77-based compression algorithm to reduce the size of input files or bundle them into a single multi-file archive. The format was a popular choice for file sharing in the early 2000s.
.ace files store data in binary format. WinAce allows users to create archives in other formats as well, such as ZIP or LHA. The .ace format itself offered a high compression ratio and speed, producing smaller output files than many contemporary alternatives. WinAce was also capable of decompressing archives such as RAR, ARC, ARJ, GZ, TAR, or ZOO, among others.
ACE 2.0 added optional Blowfish password encryption and support for multi-volume split archives (typically named .ace, .c00, .c01, and so on). Each archive header carries a ACE signature at byte offset 7, along with a CRC32 checksum for integrity verification.
WinAce was abandoned around 2007 and the format has since faded from widespread use. Support was further curtailed after the decompression library unacev2.dll was found to carry CVE-2018-20250, a path-traversal vulnerability exploited in the wild. WinRAR removed .ace support entirely in version 5.70 (2019), and today .ace files should be treated with caution.
Security & safety
RISK: HIGHACE has a serious security history. The closed-source decompression library unacev2.dll carried CVE-2018-20250, a path-traversal flaw disclosed by Check Point Research in 2019: a crafted .ace archive could write a file to an arbitrary location (e.g. the Windows Startup folder) and gain code execution. Exploits were used in real targeted attacks, and over 100 unique exploit samples appeared within a week. Because of this, WinRAR removed ACE support in v5.70 and 7-Zip never had it. Open .ace files only from sources you trust, with a fully updated extractor, and prefer extracting in a sandbox/VM. Also beware fake "ACE opener" download sites that bundle adware/PUPs - stick to PeaZip, IZArc, or The Unarchiver. After extracting, re-pack to ZIP/7z and delete the .ace.
Format details
in a nutshell- Sage ACT! / Steinberg WaveLab project - Some legacy apps used .ace for their own project/data files; unrelated to WinAce archives.
- FProt / antivirus quarantine - A few security tools historically named quarantine or temp files .ace; not user archives.
Programs that open ACE files
Windows3 apps
PeaZip
Open-source Open the .ace and Extract; PeaZip provides ACE support via its bundled backends. Update to the latest build first. 
ALZip
Freemium Open the .ace and extract; ALZip historically supports ACE among many archive formats. 
IZArc
Free Right-click the .ace > Extract Here; IZArc retains ACE extraction. Decline bundled offers during install. 
macOS1 app
The Unarchiver
Free Right-click the .ace > Open With > The Unarchiver to extract; it reads ACE among dozens of legacy formats. 
Linux2 apps
unace + Xarchiver / Engrampa
Open-source Install the 'unace' package, then open the .ace in Xarchiver/Engrampa (or run 'unace x file.ace') to extract. Technical details
deep spec| File encoding | Binary (proprietary format) |
| Byte order | Little-endian |
| MIME type | application/x-ace-compressed |
| Archive signature | "**ACE**" (ASCII) at byte offset 7 in the main header, preceded by a 4-byte CRC and 2-byte header size field |
| Compression algorithm | Proprietary LZ77-based algorithm (ACE 1.0 and ACE 2.0); historically offered a higher compression ratio than ZIP and was competitive with RAR |
| Encryption | Optional Blowfish password encryption, introduced in ACE 2.0 |
| Integrity checks | CRC32 checksum per compressed file entry plus a separate header CRC; optional recovery record for repairing damaged archives |
| Format versions | ACE 1.0 and ACE 2.0; version byte stored in the main archive header |
| Multi-volume support | Yes; split archives use the first-volume extension .ace followed by .c00, .c01, .c02, etc. |
| Typical archive size | Tens of KB to several GB; no hard size cap defined by the format |
| Platform support | Originally Windows-only (WinAce); later readable on macOS via The Unarchiver and on Linux via unace |
| Security status | CVE-2018-20250: path-traversal flaw in unacev2.dll exploited in the wild; WinRAR dropped ACE support entirely in v5.70 (2019) |
| Developer | e-merge GmbH (Marcel Lemke) |
| Format status | Abandoned; WinAce discontinued around 2007; format effectively frozen at ACE 2.0 with no active development |
| Related extensions | .c00, .c01 (additional split volumes); format largely superseded by .rar, .zip, and .7z |
| Released | 1998-1999 (ACE 1.0 / WinAce); ACE 2.0 added stronger compression |
| Latest version | ACE 2.0 (format effectively frozen; WinAce abandoned ~2007) |
ACE conversions
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