Command Injection in aiosmtplib (CVE-2026-53533)
Summary
Command injection in aiosmtplib (CVE-2026-53533). Risk of unauthorized operations or information disclosure. Exploitable via aiosmtplib. Mitigation: upgrade to 5.1.1 or later.
Original description
The description as published by the source.
Summary
aiosmtplib's SMTP.mail(), SMTP.rcpt(), SMTP.vrfy() and SMTP.expn() send the caller-supplied email address to the server without rejecting embedded CR/LF (\r\n) bytes. An address that contains a CR/LF is written verbatim onto the SMTP control connection, so the bytes after the CRLF are framed by the server as one or more additional, standalone SMTP command lines. A caller that passes an attacker-influenced sender or recipient address into mail()/rcpt() (or vrfy()/expn()) therefore allows SMTP command injection (CWE-93 / CWE-77): the attacker can smuggle arbitrary SMTP verbs such as MAIL FROM, RCPT TO, RSET, DATA, or AUTH into the session. Injected commands will cause the SMTP instance to hang, but all commands required to complete the envelope could be sent in one address string.
The SMTP.sendmail() command will pass sender and recipient addresses verbatim through to SMTP.mail() & SMTP.rcpt(), and so is also vulnerable. SMTP.send_message() is not affected.
Impact
Severity: medium. Type: SMTP protocol command injection (CWE-93 — Improper Neutralization of CRLF Sequences; CWE-77 — Command Injection).
When an application built on aiosmtplib derives the envelope sender or any recipient from data an attacker can influence (a web form etc.) and passes it to mail()/rcpt() (directly, or via sendmail()/send() without a Message object), the attacker can:
- desynchronize the command/response pipeline and ca…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
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-2026-53533 has been found in aiosmtplib.
Attackers can target a specific entry point like aiosmtplib over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade aiosmtplib to 5.1.1 or later.
If unsure, ask your IT team or search "aiosmtplib CVE-2026-53533" on the vendor's site.
CVE-2026-53533 (aiosmtplib) — CWE-77
Attack surface: aiosmtplib / RSET / DATA / AUTH
Patched: 5.1.1 — 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.
A vulnerability (CWE-77) exists in aiosmtplib. Attackers reach the vulnerable code path via aiosmtplib.
Check the vendor advisory for the affected versions of aiosmtplib. Attack surface: aiosmtplib / RSET / DATA / AUTH.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 5.1.1.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'aiosmtplib' . 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
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1Identify exposure identify
grep -r 'aiosmtplib' . | 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
aiosmtplibを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade aiosmtplib to 5.1.1ステージング環境で 5.1.1 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。
-
3Post-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。