Panic and unbounded allocation (OOM) in the CFB/OLE2 parser on malformed input

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

The Compound File Binary (OLE2) parser (`src/cfb.rs`), used when reading `.xls` and `.xlsb` workbooks and when extracting VBA projects from `.xlsx`, can panic or allocate without bound on crafted input. Both are reachable through the public reader API (`open_workbook`, `Xls::new`, `Xlsb::new`) on an attacker-supplied file. Impact is denial of service only — no memory unsafety (safe Rust turns the out-of-bounds read into a bounds-checked panic). 1. Reachable panic (out-of-bounds slice index). The directory stream is iterated with `.chunks(128)`, but `Directory::from_slice` reads fixed offsets (`buf[..64]`, `buf[116..120]`, `buf[120..128]`) without checking the chunk length. A directory stream whose length is not a multiple of 128 yields a short final chunk, causing a panic (`range end index 64 out of range for slice of length N`). `SectorSize::Small` 64-byte mini sectors are a second trigger. 2. Unbounded allocation / OOM. The DIFAT loader grows the `difat` vector without…

Published by the source

28 Oct 2026, 12:00 UTC

Last modified by the source

3 Nov 2026, 09:45 UTC

Source last checked

4 Nov 2026, 06:30 UTC

1. Revision 1 · created · 4 Nov 2026

   Published from osv record RUSTSEC-2026-0436

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: rustsec-2026-0436

Advisory: Panic and unbounded allocation (OOM) in the CFB/OLE2 parser on malformed input
IDs: rustsec-2026-0436
Record: https://patchnext.com/advisories/rustsec-2026-0436 (revision 1, source checked 4 Nov 2026, 06:30 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: calamine 0.38.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io calamine: affected >= 0.0.0-0, < 0.38.0; fixed in 0.38.0

## Suggested inspection (read-only)
- crates.io calamine: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on calamine.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/RUSTSEC-2026-0436 (OSV record RUSTSEC-2026-0436 lists affected ranges: crates.io calamine >=0.0.0-0 <0.38.0 (fixed))

Commands are suggestions: review each one before running it.