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CVE-2026-7840

UltraVNC repeater through 1.8.2.2 contains a global buffer overflow in its embedded HTTP administration server. The functions wi_senderr() and wi_replyhdr() in repeater/webgui/webutils.c write the caller-supplied HTTP request URI into a fixed 1000-byte global buffer (hdrbuf) via unchecked sprintf calls. The HTTP receive buffer accepts URIs up to approximately 150 KB (WI_RXBUFSIZE = 153600), so an unauthenticated attacker who can reach the repeater HTTP port (default TCP 80) can overflow hdrbuf b
Lifecycle PUBLISHED1 preserved revisionFact urn:baitaphish:canonical-cve-fact-revision:v2:17d8694579dfe85bef4f5354f4c4b66cb92d640bcd800997e98dfebb452b90b4
Known exploited
Not asserted
Disputed
No
Stale source
No
Conflicts
1

Preserved source conflicts

No provider value was silently selected as the winner.

cvss · 2 assertions

{"metric":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"HIGH","baseScore":9.8,"baseSeverity":"CRITICAL","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","version":"3.1"},"metric_type":"cvssV3_1"}

  • cve_program_cvelist_v5cvss
    urn:baitaphish:normalized-source-record:v2:6b4ad0238dcdd30450ac8a5e9b40d142a51fef6ebeea2b5635eb3c2014c9a280 · sha256:7ecae83a9e5e4236… · /containers/cna/metrics/0/cvssV3_1

{"metric":{"baseScore":9.3,"baseSeverity":"CRITICAL","vectorString":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","version":"4.0"},"metric_type":"cvssV4_0"}

  • cve_program_cvelist_v5cvss
    urn:baitaphish:normalized-source-record:v2:6b4ad0238dcdd30450ac8a5e9b40d142a51fef6ebeea2b5635eb3c2014c9a280 · sha256:7ecae83a9e5e4236… · /containers/cna/metrics/0/cvssV4_0

Affected products and versions

1 source assertion
{"defaultStatus":"unaffected","modules":["repeater"],"product":"UltraVNC","vendor":"uvnc","versions":[{"lessThanOrEqual":"1.8.2.2","status":"affected","version":"0","versionType":"custom"}]}
  • cve_program_cvelist_v5affected
    urn:baitaphish:normalized-source-record:v2:6b4ad0238dcdd30450ac8a5e9b40d142a51fef6ebeea2b5635eb3c2014c9a280 · sha256:7ecae83a9e5e4236… · /containers/cna/affected/0

Provider-owned CVSS observations

2 source assertions
{"metric":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"HIGH","baseScore":9.8,"baseSeverity":"CRITICAL","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","version":"3.1"},"metric_type":"cvssV3_1"}
  • cve_program_cvelist_v5cvss
    urn:baitaphish:normalized-source-record:v2:6b4ad0238dcdd30450ac8a5e9b40d142a51fef6ebeea2b5635eb3c2014c9a280 · sha256:7ecae83a9e5e4236… · /containers/cna/metrics/0/cvssV3_1
{"metric":{"baseScore":9.3,"baseSeverity":"CRITICAL","vectorString":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","version":"4.0"},"metric_type":"cvssV4_0"}
  • cve_program_cvelist_v5cvss
    urn:baitaphish:normalized-source-record:v2:6b4ad0238dcdd30450ac8a5e9b40d142a51fef6ebeea2b5635eb3c2014c9a280 · sha256:7ecae83a9e5e4236… · /containers/cna/metrics/0/cvssV4_0

CWE assertions

1 source assertion
{"cweId":"CWE-787","description":"Out-of-bounds Write","lang":"en","type":"CWE"}
  • cve_program_cvelist_v5cwe
    urn:baitaphish:normalized-source-record:v2:6b4ad0238dcdd30450ac8a5e9b40d142a51fef6ebeea2b5635eb3c2014c9a280 · sha256:7ecae83a9e5e4236… · /containers/cna/problemTypes/0/descriptions/0

Source references

3 source assertions
{"name":"UltraVNC source repository","tags":["product"],"url":"https://github.com/ultravnc/UltraVNC"}
  • cve_program_cvelist_v5reference
    urn:baitaphish:normalized-source-record:v2:6b4ad0238dcdd30450ac8a5e9b40d142a51fef6ebeea2b5635eb3c2014c9a280 · sha256:7ecae83a9e5e4236… · /containers/cna/references/1
{"name":"UltraVNC project page","tags":["vendor-advisory"],"url":"https://uvnc.com/"}
  • cve_program_cvelist_v5reference
    urn:baitaphish:normalized-source-record:v2:6b4ad0238dcdd30450ac8a5e9b40d142a51fef6ebeea2b5635eb3c2014c9a280 · sha256:7ecae83a9e5e4236… · /containers/cna/references/0
{"url":"https://www.securin.io/zero-days/cve-2026-7840-pre-auth-global-buffer-overflow-repeater-http-admin-ultravnc"}
  • cve_program_cvelist_v5reference
    urn:baitaphish:normalized-source-record:v2:6b4ad0238dcdd30450ac8a5e9b40d142a51fef6ebeea2b5635eb3c2014c9a280 · sha256:7ecae83a9e5e4236… · /containers/cna/references/2

Attribution and limitations

  • CVE Program CVEList V5: Reproduce the MITRE copyright designation and CVE license in copies. Source →

Provider severity values are preserved separately. Baitaphish does not convert them into a risk rating, infer affected products, or treat EPSS as observed exploitation.

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