Description
The prompt only describes the first Windows Print Spooler remote code execution vulnerability disclosed in 2021. Identify the matching CVE and submit it in the picoCTF flag format.
Setup
The challenge prompt asks: "Can you reproduce the CVE for the first Windows Print Spooler Remote Code Execution Vulnerability of 2021?"
Search the literal phrasing of the prompt - every result references PrintNightmare.
Open the CVE database entry to verify the identifier CVE-2021-34527.
Wrap that ID in the picoCTF format: picoCTF{CVE-2021-34527} (dashes preserved from the CVE ID).
Solution
Want to try it yourself first?
The guided walkthrough reveals hints one step at a time.
Step 1
Pivot on the clueObservationI noticed the prompt named a specific product (Windows Print Spooler), a vulnerability class (remote code execution), and a year (2021), which suggested searching those exact terms to find the canonical CVE entry from a public database like MITRE or cve.org.Search the literal prompt. Every top result names PrintNightmare; cross-check against MITRE/cve.org to confirm CVE-2021-34527.What didn't work first
Tried: Searching for 'Windows Print Spooler vulnerability 2021' and landing on CVE-2021-1675 instead.
CVE-2021-1675 was an earlier, related Print Spooler patch released in June 2021. It was initially mislabeled as the same bug but only fixed a privilege escalation, not full unauthenticated RCE. The challenge asks for the first full remote code execution CVE, which is CVE-2021-34527. Cross-referencing multiple sources (MITRE, Microsoft advisory, CISA) will consistently name CVE-2021-34527 as PrintNightmare's RCE identifier.
Tried: Searching broadly for 'Print Spooler CVE' without the year and finding a different year's entry.
The Print Spooler service has had many CVEs across multiple years. Without anchoring the search to 2021 and specifically remote code execution, results may surface older or unrelated bugs. Adding 'RCE 2021' and 'PrintNightmare' to the search immediately narrows it to the correct entry.
Learn more
Sample search verification. Querying "Windows Print Spooler RCE 2021" returns Microsoft Security Update Guide, Project Zero, CISA, and most major vendors - all naming the bug PrintNightmare and pointing at CVE-2021-34527. Multiple independent sources naming the same CVE is the signal that you have the right one (not a related but distinct bug like CVE-2021-1675, which was the partial fix that didn't actually fix it).
CVE (Common Vulnerabilities and Exposures) is the public catalog maintained by MITRE. Each entry has a unique
CVE-YEAR-NUMBERID. PrintNightmare(CVE-2021-34527) hit the Windows Print Spooler service - which runs as SYSTEM and is enabled by default - allowing unauthenticated remote code execution. It became notorious because a PoC leaked before Microsoft's patch.The skill being tested is OSINT: given a description, find the canonical identifier. This is what defenders do daily when correlating threat intel against scanner output.
Step 2
Submit the CVEObservationI noticed the challenge flag format requires wrapping an identifier in picoCTF{...}, and CVE IDs always include dashes as part of their canonical form, which suggested preserving the dashes from CVE-2021-34527 exactly when constructing the flag.Wrap the ID in the picoCTF format, keeping the dashes from the CVE ID:picoCTF{CVE-2021-34527}.What didn't work first
Tried: Submitting just the number portion without dashes, like picoCTF{CVE202134527}.
CVE IDs are always written with their dashes intact as part of the canonical format (CVE-YEAR-NUMBER). Dropping the dashes produces an unrecognized identifier. The flag must preserve the exact formatting: picoCTF{CVE-2021-34527}.
Tried: Submitting the vulnerability name 'PrintNightmare' as the flag instead of the CVE ID.
PrintNightmare is the colloquial nickname for this vulnerability, not its official identifier. The challenge asks for the CVE number, which is the standardized catalog ID. The correct answer wraps the CVE ID - not the nickname - in the picoCTF flag format.
Learn more
The CVE ID lives directly in the URL path on cve.org:
https://www.cve.org/CVERecord?id=CVE-2021-34527. Pull the value of theidquery parameter and you have your answer. NVD does the same:https://nvd.nist.gov/vuln/detail/CVE-2021-34527.Resources for CVE work: cve.org (the canonical MITRE list), nvd.nist.gov(adds CVSS scores), and vendor advisories (Microsoft's Security Update Guide for this one). CVSS rates severity 0-10; PrintNightmare scored 8.8 to 9.8 depending on attack vector. Defenders patch the 9.x scores first.
Other high-profile CVEs worth recognizing: Log4Shell (CVE-2021-44228), EternalBlue (CVE-2017-0144), Heartbleed (CVE-2014-0160).
Interactive tools
- Cyclic Pattern GeneratorGenerate de Bruijn cyclic patterns and find buffer overflow offsets. The browser equivalent of pwntools cyclic and cyclic_find.
Flag
Reveal flag
picoCTF{CVE-2021-34527}
This is the PrintNightmare vulnerability affecting the Windows Print Spooler service. The CVE ID appears in the cve.org URL path.