Vulnerability in smallvec (CVE-2021-25900)

Summary

Vulnerability in smallvec (CVE-2021-25900). Successful exploitation can lead to full system takeover. Exploitable via insert_many. Mitigation: upgrade to 0.6.14, 1.6.1 or later.

Original description

The description as published by the source.

A bug in the SmallVec::insert_many method caused it to allocate a buffer that was smaller than needed. It then wrote past the end of the buffer, causing a buffer overflow and memory corruption on the heap.

This bug was only triggered if the iterator passed to insert_many yielded more items than the lower bound returned from its size_hint method.

The flaw was corrected in smallvec 0.6.14 and 1.6.1, by ensuring that additional space is always reserved for each item inserted. The fix also simplified the implementation of insert_many to use less unsafe code, so it is easier to verify its correctness.

Thank you to Yechan Bae (@Qwaz) and the Rust group at Georgia Tech’s SSLab for finding and reporting this bug.

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2021-25900 has been found in smallvec.
Attackers can target a specific entry point like insert_many over the network to misuse the product.
Successful exploitation can lead to full system takeover.
What to do: upgrade smallvec to 0.6.14, 1.6.1 or later.
If unsure, ask your IT team or search "smallvec CVE-2021-25900" on the vendor's site.

CVE-2021-25900 (smallvec)
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: insert_many / size_hint
Patched: 0.6.14, 1.6.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (unclassified) exists in smallvec. Attackers reach the vulnerable code path via insert_many without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of smallvec. Attack surface: insert_many / size_hint.

🔥 Severity

Severity: ?. Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to 0.6.14, 1.6.1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'smallvec' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

1
Identify exposure identify
```
grep -r 'smallvec' . | grep -v node_modules
```
リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で smallvec を grep し、稼働しているサービス・バージョンを把握する。
2
Apply patch patch
```
Upgrade smallvec to 0.6.14, 1.6.1
```
ステージング環境で 0.6.14, 1.6.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
3
Post-deployment verification verify
```
Confirm patched version is live in production
```
パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

crates.io smallvec

[{"type":"SEMVER","events":[{"introduced":"0.6.3"},{"fixed":"0.6.14"},{"introduced":"1.0.0"},{"fixed":"1.6.1"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

Ubuntu UBUNTU-CVE-2021-25900 rust-smallvec

References

advisory rustsec.org
package crates.io
report github.com