Session data theft via reflected Autodiscover script injection
Published Nov 10, 2021 · Updated Aug 19, 2026
Reflected XSS in affected Microsoft Exchange Server 2013, 2016, and 2019 builds allows remote attackers to steal session data via a crafted URL. The Autodiscover autodiscover.json path places attacker-controlled input into HandleBackEndCalculationException output without adequate validation or encoding. Exploitation needs no account but requires a user to open the crafted link, after which script runs in that user's browser context and can expose session credentials.
Summary
What happened
Reflected XSS in affected Microsoft Exchange Server 2013, 2016, and 2019 builds allows remote attackers to steal session data via a crafted URL. The Autodiscover autodiscover.json path places attacker-controlled input into HandleBackEndCalculationException output without adequate validation or encoding. Exploitation needs no account but requires a user to open the crafted link, after which script runs in that user's browser context and can expose session credentials.
The record
- CVE
- CVE-2021-41349
- Published
- Nov 10, 2021
- Updated
- Aug 19, 2026
- Vendor
- Microsoft
- Product
- Microsoft Exchange Server 2016 Cumulative Update 21
- Classifications
- CWE-79, CAPEC-591, T1204.001
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Nov 10, 2021CVE publishedPublication date reported by the CVE source.
- Aug 19, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=15.01.0 <15.01.2308.020
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- ProjectDiscovery CVE-2021-41349 Nuclei templateproof of concept · unverified
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
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