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MediumCISA KEVExploited in the wildPublic exploit

Post-auth arbitrary file write in Microsoft Exchange Server (ProxyShell)

IdentifiersCVE-2021-31207CWE-434· Unrestricted Upload of File with…

CVE-2021-31207 is a Microsoft Exchange Server vulnerability in the ProxyShell attack chain affecting on-premises Exchange Server 2013, 2016, and 2019, particularly Exchange Client Access Server functionality. The provided content consistently describes it as a post-authentication arbitrary file write issue that can be abused to write attacker-controlled files, including ASPX webshells, to Exchange/IIS-accessible directories. In observed exploitation, attackers abused Exchange management functionality such as New-MailboxExportRequest and, in some detections, New-ExchangeCertificate, to place webshell content into web-accessible paths. Although Microsoft’s title for the CVE is 'Security Feature Bypass,' the supplied material specifically characterizes the operational flaw as a post-auth arbitrary-file-write primitive that is commonly chained with CVE-2021-34473 and CVE-2021-34523 as part of ProxyShell.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation enables an authenticated attacker to write arbitrary files to locations reachable by IIS/Exchange, commonly resulting in deployment of one or more webshells. In practice, this is used to convert Exchange access into remote code execution on the server, often with SYSTEM-level execution when chained through the full ProxyShell sequence. Follow-on impact described in the content includes persistent server compromise, execution of Exchange PowerShell cmdlets, mailbox access, credential theft, lateral movement, ransomware deployment, and broader domain compromise.

Mitigation

If you can’t patch tonight, do this now.

If immediate patching is not possible, reduce or eliminate direct internet exposure of on-premises Exchange Client Access services, especially those exposed over TCP 443. Monitor and alert on suspicious requests associated with ProxyShell activity and on Exchange management events involving New-MailboxExportRequest and New-ExchangeCertificate. Hunt for webshell artifacts in common Exchange/IIS paths such as inetpub\wwwroot\aspnet_client\ and Exchange FrontEnd HttpProxy directories, and investigate PowerShell spawned by w3wp.exe or anomalous Exchange Management log entries. Restrict administrative and Exchange management access where possible and apply compensating controls around externally reachable Exchange infrastructure.

Remediation

Patch, then assume compromise.

Apply Microsoft's security updates for Exchange that address ProxyShell, including the May 2021 update referenced as KB5003435 for CVE-2021-31207, and ensure all relevant Exchange cumulative and security updates are current across Exchange Server 2013, 2016, and 2019. Because CVE-2021-31207 is typically exploited as part of the ProxyShell chain, remediation should include patching the associated vulnerabilities CVE-2021-34473 and CVE-2021-34523 as well. Review Exchange servers for indicators of compromise after patching, including unexpected ASPX files in Exchange/IIS web directories and suspicious Exchange management activity involving mailbox export operations.
PUBLIC EXPLOITS

Exploits

4 valid exploits after Mallory filtered fakes, detection scripts, and README-only repos (1 hidden).

VALID 4 / 5 TOTALView more in app
abyss-c2MaturityPoCVerified exploit

This repository is a multi-module Python offensive framework centered on exploiting HiSilicon DVR/NVR/IP camera devices via CVE-2020-25078, then managing compromised hosts through a Flask/SocketIO web panel. It is not a simple single-file PoC: it includes a control server (server.py), persistence and post-exploitation tooling, credential attacks, recon modules, web vulnerability scanners, network service checks, pivoting, reverse shell support, and a SQLite-backed datastore. Core exploit logic is in exploit.py and scanner.py. exploit.py probes numerous traversal/disclosure paths such as /../../.../mnt/mtd/Config/Account1 and related config/system files, parses returned content with multiple regex patterns to recover credentials, fingerprints device families, and falls back to known default credentials when disclosure succeeds but parsing does not. scanner.py operationalizes this by scanning IPs/CIDRs and common ports, checking liveness, fingerprinting likely cameras, invoking the CVE-2020-25078 checks, and storing recovered credentials in cameras.db. Post-exploitation capability is substantial. telnet_client.py provides raw Telnet login and command execution. botnet.py fans out commands across stored hosts. persistence.py installs SSH authorized_keys, cron, rc.local, init.d, systemd, inittab telnetd, and bind-shell style persistence. reverse_shell.py generates many Linux/IoT reverse shell one-liners and runs listeners. pivot_chain.py and socks_pivot.py support chained execution and local SOCKS5 pivoting through compromised hosts. Additional modules broaden scope beyond the HiSilicon exploit: brute.py and cred_spray.py perform credential attacks across Telnet, SSH, FTP, HTTP, SMB, databases, VNC, LDAP, WinRM, and more; network_exploit.py checks for exposed/misconfigured services and some well-known vulnerabilities such as MS17-010 and BlueKeep; web_exploit.py, web_cves.py, web_bugs.py, and web_brute.py scan websites for exposed files, CMS fingerprints, generic bug classes, and multiple CVE signatures. Recon/intel support includes ASN, DNS, GeoIP, JARM, WAF detection, proxy/Tor rotation, screenshot grabbing from camera snapshot endpoints, and Telegram/Discord/AbuseIPDB integrations. The repository structure is coherent and functional, with many CLI-capable modules and a central web UI in templates/index.html. Overall, this is an operational exploit-and-post-exploitation toolkit focused on HiSilicon IoT devices but expanded into a broader C2-style offensive platform.

flags-altDisclosed May 20, 2026pythonhtmlnetworkweblocal
ProxyHellMaturityPoCVerified exploit

Small single-script Python exploit repository for Microsoft Exchange ProxyShell-style exploitation. The repository contains one executable code file, proxyhell_revisited.py, plus a short README, license, and .gitignore. The script uses requests and disables TLS verification warnings, indicating intended direct interaction with remote Exchange servers over HTTPS/HTTP. Its workflow is: (1) send a crafted Autodiscover request to leak the target mailbox LegacyDN using a supplied valid email address; (2) send a crafted MAPI request to extract a user SID from the Exchange response; (3) forge a serialized Windows token containing the recovered SID plus privileged group SIDs; (4) submit a SOAP/PowerShell remoting request with the forged token to execute a PowerShell command that writes a base64-decoded ASPX/JScript webshell into the IIS aspnet_client directory; and (5) print the resulting webshell URL for follow-on command execution. The embedded payload is not just a detector: it is a functional post-exploitation webshell that runs arbitrary commands via cmd.exe and returns output. The script also supports a limited --check mode that only tests the LegacyDN leak path and reports likely vulnerability to CVE-2021-34473. Overall, this is an operational PoC exploit for remote Exchange compromise and webshell deployment, not a framework module and not merely a README or scanner.

LoqueseamevalevergDisclosed Mar 16, 2026pythonnetwork
proxyshellMaturityPoCVerified exploit

This repository contains a Python-based Proof of Concept (PoC) exploit for the ProxyShell vulnerability chain affecting Microsoft Exchange Server (CVE-2021-34473, CVE-2021-34523, CVE-2021-31207). The main exploit script, 'exchange_proxyshell.py', automates the exploitation process by targeting Exchange's Autodiscover, MAPI, ECP, and EWS endpoints. It first enumerates users and emails from Active Directory, discovers LegacyDNs, and then abuses the ProxyShell vulnerabilities to obtain a valid access token. Using this token, the script establishes a PowerShell remoting session to the Exchange server, allowing the attacker to execute arbitrary commands. The exploit is operational and provides remote code execution capabilities. The repository is well-structured, with a detailed README explaining usage, features, and mitigation steps. No hardcoded IPs or domains are present; the target Exchange server is specified by the user at runtime.

horizon3aiDisclosed Sep 4, 2021pythonnetwork
ProxyVulnsMaturityPoCVerified exploit

This repository contains operational exploit scripts for multiple high-profile Microsoft Exchange Server vulnerabilities: ProxyLogon (CVE-2021-26855, etc.), ProxyOracle (CVE-2021-31196), and ProxyShell (CVE-2021-34473, CVE-2021-31207). The structure includes four main Python scripts: - 26855.py: Implements the ProxyLogon exploit chain, culminating in the upload of a JScript webshell (api.aspx) to the Exchange server by abusing the OAB virtual directory. It automates the process of obtaining necessary tokens and SIDs, and provides a final webshell URL for remote code execution. - 31196.py: Implements the ProxyOracle padding oracle attack, allowing extraction of plaintext credentials from encrypted session cookies by exploiting a padding oracle vulnerability in OWA. It requires a valid 'cadata' cookie and outputs the decrypted username and password. - 34473.py: Implements the ProxyShell exploit chain, allowing remote PowerShell command execution on the Exchange server. It automates the process of obtaining a valid CommonAccessToken and then uses pypsrp to execute arbitrary PowerShell scripts remotely. - 31207.py: Works with 34473.py to deliver arbitrary files (e.g., malicious PDFs) to user mailboxes and then exports mailbox contents to a specified UNC path, leveraging Exchange's mailbox export features. A users.txt file provides a list of default or known usernames to assist in the exploitation process. The README.md gives usage instructions and references for each exploit. The scripts are operational and automate the full exploitation process, including credential extraction, webshell upload, remote command execution, and file delivery. The main attack vector is network-based, targeting exposed Exchange web services (ECP, OWA, Autodiscover, EWS, and PowerShell endpoints).

hosch3nDisclosed Apr 14, 2021pythonnetwork
EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType
Microsoft CorporationExchange Serverapplication

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What this page doesn’t show

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Exposure mapping

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Threat actor evidence56

Every observed campaign linking this CVE to a named adversary.

Associated malware13

Malware families riding this exploit, with evidence and IOCs.

Detection signatures1

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Vendor-by-vendor mapping

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Social activity2

Community discussion across Reddit, Mastodon, and other social sources.