- Reported
-
- Issued
-
- Package
-
zstd-safe
(crates.io)
- Type
-
Vulnerability
- Categories
-
- Keywords
-
#uninitialized-memory
#decompression
#legacy
- References
-
- Patched
-
- Unaffected
-
- Affected Functions
- Version
zstd_safe::DCtx::decompress_stream-
Description
When decompression fails inside a legacy (zstd v0.4 to v0.7) frame, the
bundled zstd library reports the output buffer as fully written although
nothing was written. DCtx::decompress_stream committed that position even
on error, and for a Vec<u8> destination this extended the vector's length
over uninitialized memory.
Legacy support is enabled by default. A 5- or 6-byte corrupt legacy frame is
enough: through zstd::stream::write::Decoder, up to 32 KiB of stale heap
memory is then passed to the wrapped writer on the next write() or
flush(), or when an auto_flush()/on_flush() decoder is dropped. Whether
this reaches an attacker depends on where the application sends the
decompressed output. zstd::stream::read::Decoder, zstd::decode_all and
the bulk API are not affected.
Before zstd-safe 4.0.0, output buffers could only be initialized slices.
The zstd crate's own writer had the same flaw from 0.4.22 to 0.7.x, which is
covered by a separate advisory.
The flaw was corrected by only committing the buffer positions of a
successful call.
Advisory available under CC0-1.0
license.