Is zlib1.dll safe?
No engines detected malware, the CD PROJEKT signature verifies correctly, and broad historical prevalence plus five consistent signer matches strongly support a benign library.
All 74 engines returned without a malicious or suspicious detection, including 17 tier-1 engines. The verified CD PROJEKT S.A. signature, 433-source prevalence, and five prior benign signer matches strongly support this DLL as legitimate software, despite one uncorroborated sandbox technique.
77f76feece34b8c703…7a0062eac947baRecommended next actions
Before using
Use it only as part of software obtained from the developer's official site or another source you independently trust.
If you already used it
Keep normal device protection enabled and stop if the file behaves unexpectedly.
Intelligence
The saved assessment, checked against the scan evidence and recorded coverage.
The reasoning behind this verdict
This section explains the evidence supporting the verdict and keeps conflicting or missing signals visible.
All 74 engines returned without a malicious or suspicious detection, including 17 tier-1 engines. The verified CD PROJEKT S.A. signature, 433-source prevalence, and five prior benign signer matches strongly support this DLL as legitimate software, despite one uncorroborated sandbox technique.
The antivirus results are uniformly favorable, with 0 of 74 engines flagging the DLL and all 17 tier-1 engines returning no detection. Its signature verifies as CD PROJEKT S.A., and there is no conflict between the claimed brand and signer. The sample is established rather than newly observed, with 433 sources and 485 submissions over 431 days. Five prior files bearing the same signer received benign assessments and had no detections among 74 engines. One sandbox mapped activity to T1562.001, but it produced no malicious sandbox verdict, no malicious child was identified, and no external intelligence source corroborated a threat.
What We Detected
No antivirus engine flagged this DLL: 0 of 74 reported it as malicious or suspicious, and all 17 tier-1 engines returned no detection. The file carries a verified signature from CD PROJEKT S.A., with no detected brand mismatch. It is also well established, appearing across 433 sources and 485 submissions over 431 days.
Threat Behavior
One completed sandbox run did not produce a malicious verdict. It mapped one action to T1562.001, but that isolated signal was not corroborated by engine detections, malicious persistence, external intelligence, or the nine inspected child hashes. No network contacts were recorded during the run; however, a separate host-reputation cross-check was not available.
What To Do Now
The evidence is consistent with a legitimate signed library distributed with CD PROJEKT software. Keep endpoint protection enabled and obtain the DLL from the official game installation or distribution channel if its origin is uncertain.
Where this verdict could be wrong3 caveats
- behaviour.offensiveTechniques includes T1562.001, but the single sandbox produced no malicious verdict and the technique lacks corroboration from engines or external intelligence.
- signing.signerStats.totalSamples=1 provides limited direct publisher history, although five signer-matched prior decisions independently support the same publisher.
- contactedHosts is null, so no complete host-reputation cross-check is available; the sandbox recorded no contacted domains, IP addresses, or URLs.
These are the assessment's weak points. If you believe one applies to your file, report the verdict and we'll re-review it.
- 0/74 antivirus engines reported a malicious or suspicious result.
- All 17 tier-1 engines reported no detection.
- Verified digital signature from CD PROJEKT S.A.
- Five of five prior signer-matched files received benign assessments.
- Observed across 433 sources and 485 submissions over 431 days.
- One sandbox mapped activity to T1562.001, an endpoint-protection impairment technique.
- Direct signer statistics cover only one historical sample.
- No complete contacted-host reputation cross-check is available.
The file can remain in place when it came from a legitimate CD PROJEKT installation. If its source is unknown, restore it from the official installer rather than downloading a replacement from an unaffiliated site.
Coverage & freshness
Complete means the check returned a usable result. It does not mean the file is safe.
Antivirus
Complete0 of 74 engines flagged the file.
Sandbox
Complete1 isolated runtime environment contributed observations.
Network
Not runNo contacted-host reputation check is recorded.
No timestamp recordedYARA
CompleteRule evaluation completed with no recorded matches.
External intel
Complete3 of 3 independent reference sources completed.
Behavior
Plain-English impact first, then the observed runtime evidence.
Runtime flight recorder
Capture complete- 1isolated sandbox run
- 11MITRE ATT&CK techniques
- 15spawned processes
- 0network contacts
- 40filesystem & mutex artifacts
Attack story
Runtime observations grouped by analysis stage. Arrows organize the stages; they do not claim chronology or causality.
Input file
The submitted object
- FileObserved
zlib1.dll
77f76feece34b8c70393865ec896a188a3ee820b5c65e677b87a0062eac947ba
01Uploaded file
Processes
Runtime execution
- ProcessObserved
Observed process
"C:\Windows\sysnative\rundll32.exe" "C:\Users\<USER>\Desktop\zlib1.dll",#1
02Isolated runtime analysis - ProcessObserved
Observed process
C:\Windows\system32\WerFault.exe -u -p 6392 -s 500
03Isolated runtime analysis - +1 more recorded observation in Analyst mode
Files
Created or changed
- Written fileObserved
Temp
C:\ProgramData\Microsoft\Windows\WER\Temp
04Isolated runtime analysis - Written fileObserved
605cdcec-3669-4cae-b169-6c3b357db2d4
C:\ProgramData\Microsoft\Windows\WER\Temp\605cdcec-3669-4cae-b169-6c3b357db2d4
05Isolated runtime analysis - +1 more recorded observation in Analyst mode
5 recorded facts from one runtime window. Every fact remains independently traceable in Analyst mode.
What this file did when executed
This file was detonated in 1 sandbox and its runtime behaviour was observed.
Adversary techniques mapped to the MITRE ATT&CK framework.
- C:\ProgramData\Microsoft\Windows\WER\Temp
- C:\ProgramData\Microsoft\Windows\WER\Temp\605cdcec-3669-4cae-b169-6c3b357db2d4
- C:\ProgramData\Microsoft\Windows\WER\ReportQueue
- C:\ProgramData\Microsoft\Windows\WER\Temp\12e7456e-bc7d-4727-a6f4-2832545a67f4
- C:\ProgramData\Microsoft\Windows\WER\ReportArchive
- C:\ProgramData\Microsoft\Windows\WER\Temp\WERCAA3.tmp
- C:\ProgramData\Microsoft\Windows\WER\Temp\WERD3CB.tmp
- C:\ProgramData\Microsoft\Windows\WER\Temp\WERD591.tmp
- C:\ProgramData\Microsoft\Windows\WER\Temp\WERCAA3.tmp.dmp
- C:\ProgramData\Microsoft\Windows\WER\Temp\WERD3CB.tmp.WERInternalMetadata.xml
- Local\WERReportingForProcess6392
- Global\AmiProviderMutex_InventoryApplicationFile
- Global\36d33584-9ad3-446e-bb91-32b9f10e5cec
- \Sessions\1\BaseNamedObjects\Local\SessionImmersiveColorMutex
- \Sessions\1\BaseNamedObjects\Local\WERReportingForProcess7156
Files this sample writes at runtime
This file drops 9 children at runtime. None are currently flagged malicious in our cache.
- b9fe1b21c38cea57c4ca…010863Never scannednever seen before
- 2b640e6ae88f90082424…9170feNever scannednever seen before
- 980045627d97072077a0…349bf8Never scannednever seen before
- 2fb204c7a23d0be833c0…8ae90bNever scannednever seen before
- 6419ede56d0dc6345efa…ec7d6fNever scannednever seen before
- f72575e959e2203c5fc6…44a2f7Never scannednever seen before
- 3afd20373586c539bb8e…e09fbdNever scannednever seen before
- add488f201b51afae74b…4909fdNever scannednever seen before
- 249d2bbb5f0ea89c30fb…7244f0Never scannednever seen before
Detection & Forensics
Consensus, attribution, signatures, code structure, prevalence, and identity.
Evidence integrity
Chain of custody for the facts preserved in this report.
- 0rule hits recorded
- 0 / 74engines flagged
- 433sources in submission history
Why these facts are shown
Each statement identifies whether it was directly recorded or derived from saved scan facts.
- 01
0 of 74 antivirus engines flagged the file.
Verdict inputView chapterProvenanceObservedSourceAntivirus analysisObserved at - 02
The hash has a long, established submission history across 433 sources.
Verdict inputView chapterProvenanceDerivedSourceSubmission historyObserved at - 03
The file has a valid code signature from CD PROJEKT S.A..
ProvenanceObservedSourceCode-signing metadataObserved at - 04
Scanned file: zlib1.dll — 77f76feece34b8c70393865ec896a188a3ee820b5c65e677b87a0062eac947ba
ProvenanceObservedSourceUploaded fileObserved at - 05
Observed process — "C:\Windows\sysnative\rundll32.exe" "C:\Users\<USER>\Desktop\zlib1.dll",#1
ProvenanceObservedSourceIsolated runtime analysisObserved at - 06
Observed process — C:\Windows\system32\WerFault.exe -u -p 6392 -s 500
ProvenanceObservedSourceIsolated runtime analysisObserved at - 07
File written: Temp — C:\ProgramData\Microsoft\Windows\WER\Temp
ProvenanceObservedSourceIsolated runtime analysisObserved at - 08
File written: 605cdcec-3669-4cae-b169-6c3b357db2d4 — C:\ProgramData\Microsoft\Windows\WER\Temp\605cdcec-3669-4cae-b169-6c3b357db2d4
ProvenanceObservedSourceIsolated runtime analysisObserved at
Detection sources at a glance
The available sources did not agree on a named threat category.
MalwareBazaar, YARAify, and CIRCL hashlookup completed and returned no entries for this hash.
YARA rules
No matchesThe rule pass completed without a saved public match.
0 of 74 engines flagged this file
View all 74 engine results
Section entropy & packers
No high-entropy executable section or known packer signature was detected. Data and resource sections can still have high entropy without indicating packed code.
How widely this file has been seen
Widely seen in the wild for a long time. High prior this is legitimate; isolated detections on common-old files are usually false positives.
Fingerprint and provenance
- File name
- zlib1.dll
- Format
- Win32 DLL
- Code signing
- Signature valid: CD PROJEKT S.A.
- Size
- 132.1 KB
- Last analyzed
- Sep 23, 2026, 4:49 AM UTC
77f76feece34b8c70393865ec896a188a3ee820b5c65e677b87a0062eac947baSafety & FAQ
Complete recovery guidance and answers for the next decision.
What to do now
This file appears low risk based on the evidence available now.
- Recovery step 01
Use it only as part of software obtained from the developer's official site or another source you independently trust.
- Recovery step 02
A clean result reduces known risk, but it cannot guarantee that every new or targeted threat has been detected.
- Recovery step 03
Keep your antivirus and Windows updates switched on so you stay protected.
Safety FAQ
Direct answers grounded in the saved verdict and evidence in this report.
Is zlib1.dll safe?
What is zlib1.dll?
How many antivirus engines detected zlib1.dll?
Is zlib1.dll digitally signed?
What is the SHA-256 hash of zlib1.dll?
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How up to date is this analysis of zlib1.dll?
Community
Member reviews and reports for this exact file hash.