A 512-byte workbook can provoke a multi-gigabyte allocation and abort the process

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Affected versions passed caller-supplied bytes to `calamine`'s `Xlsx::new` without first checking that they were a ZIP archive. `Xlsx::new` tests for password protection on its first line, which parses the input as an OLE/CFB container, and a sector-count field read from the file's own header reaches `Vec::with_capacity` without being checked against the file's actual length. A 512-byte input can therefore request several gigabytes; 9,261,285,372 bytes was measured. **The oversized allocation is always attempted. Whether it aborts depends on what the allocator can satisfy.** On a large host with overcommit the reservation is granted untouched and the call returns an ordinary "not an xlsx file" error, which looks like a malformed file being correctly rejected. Under a memory limit the same bytes give `memory allocation of N bytes failed` and the process aborts, which is not a `Result` a caller can handle. Containers with a memory limit, small hosts and CI runners are where this lands, so testing on a development machine can wrongly suggest the crate is unaffected. Every entry point reaches it, not only `compare_bytes`: the path- and reader-based APIs funnel through the same internal open. Neither `Limits::default()` nor `Limits::hardened()` prevents it, because `max_input_bytes` bounds the length of the input while the allocation's size comes from a field inside it. Fixed in 3.2.0, which declines input that does not begin with the ZIP magic before the parser sees it, removing the path rather than bounding it. Callers who cannot upgrade can apply the same check before calling this crate. The underlying defect is in `calamine`, reported there independently as [tafia/calamine#714](https://github.com/tafia/calamine/issues/714) and unfixed at the time of writing. It is reachable from any crate that opens untrusted bytes with `Xlsx::new`.

Source published

29 Sep 2026 12:00:00 UTC

Source modified

1 Oct 2026 07:45:02 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

OSV · upstream source license applies

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CVSS_V3 · CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H