# RUSTSEC-2026-0220: Uint shift operations: incorrect overflow flags and truncated shift amounts

> Incorrect overflow flags and truncated shift amounts in Uint operations can cause infinite loops or incorrect results when processing untrusted input.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Jul 2026

## What is RUSTSEC-2026-0220?

RUSTSEC-2026-0220 is a vulnerability in ruint, published on 8 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

`Uint::overflowing_shl`/`overflowing_shr` returned false-negative overflow
flags. `overflowing_shl` missed bits shifted above `BITS` but within the top
limb (non-limb-aligned widths such as `U160`), and limbs wholly discarded by
shifts >= 64; `overflowing_shr` missed wholly discarded low limbs. Shifted
values were correct; only the flag was wrong.

The wrong flag propagates: `checked_shl`/`checked_shr` return `Some` instead
of `None`, `strict_*` fail to panic, and `saturating_*` return a wrapped
value instead of saturating. The incorrect `checked_shl` result causes
`to_base_be` (and string formatting) to loop forever on no-alloc builds for
non-limb-aligned widths — a denial of service if formatting is reachable
from untrusted input.

Separately, `wrapping_shl`/`wrapping_shr` on 64/128/256-bit types truncated
the shift amount modulo 2^32, so shifts >= 2^32 returned an incorrectly
wrapped value instead of zero; on 32-bit targets the generic path also
truncated 64-bit shift amounts.

Callers using checked or saturating shift semantics on untrusted shift
amounts may compute incorrect results.

## Which versions are affected by RUSTSEC-2026-0220?

1 open source package ship an affected version, including ruint.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `ruint` | crates.io | From 0.0.0-0 | 1.20.0 |

## How do I fix RUSTSEC-2026-0220?

Upgrade ruint to 1.20.0 or later.

## Is RUSTSEC-2026-0220 being exploited?

There is no known exploitation of RUSTSEC-2026-0220 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0220 and fix it if it is affected.

What it is: RUSTSEC-2026-0220 is a vulnerability in ruint, published on 8 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of RUSTSEC-2026-0220 in the wild and no public exploit code.

Affected packages and fixed versions:
- ruint (crates.io): affected from 0.0.0-0; fixed in 1.20.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/RUSTSEC-2026-0220/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0220/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0220

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0220/
Summaries are generated and may contain mistakes; the official description above is the record.