CVE-2026-44042: UltraVNC repeater wi_uudecode off-by-one in base64 decode boundary check
Noroxi assessment
Priority: Monitor (action score 14/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 0.49% (FIRST EPSS).
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
- According to the record, no fixed version is available yet.
Low priority for now. Update when a fix is released; follow the vendor's advisory.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
UltraVNC repeater through 1.8.2.2 contains an off-by-one error in the Base64 decode helper used for HTTP Basic authentication. In repeater/webgui/webutils.c:817, the wi_uudecode() function checks whether the input length exceeds the output buffer with a strict greater-than comparison (>), while the correct check should be greater-than-or-equal (>=). When strlen(authdata) equals sizeof(decode), the decoded output length (approximately 3/4 of input) does not overflow the buffer in current practice because the outer HTTP request bounds constrain the Authorization header. However, the defective check leaves a latent off-by-one condition that could become exploitable if the buffering constraints change. The current risk is limited to a one-byte write at the boundary of a 1024-byte stack buffer under constrained conditions.
- Published
- Jul 1, 2026
- Updated
- Oct 25, 2026
- EPSS
- 0.4% · 42th percentile
- CWE
- CWE-193
Report tools
Action score
14
Low priority for now.
- CVSS
- 14 / 40 · 3.7 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.4%
CISA SSVC decision
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- 3.7
- CNA · securin
- 3.7
- agree
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- No fixed version yet
If any of these changes, we'll tell you in the daily email digest.
Is your version affected? Check itNoroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| uvnc | ultravnc | cpe:2.3:a:uvnc:ultravnc |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- uvnc ultravncup to 1.8.2.2 inclusive
Versions reported by the vendor
Affected version ranges reported by the assigning authority (securin). Independent of NVD's CPE analysis and usually ahead of it.
uvnc UltraVNC
- up to and including 1.8.2.2affected
Same product
uvnc: all recordsOther highest-scoring records for the same primary product.
- CVE-2019-8274UltraVNC revision 1211 has a heap buffer overflow vulnerability in VNC server code inside file transfer offer handler, which can…41Plan
- CVE-2019-8273UltraVNC revision 1211 has a heap buffer overflow vulnerability in VNC server code inside file transfer request handler, which can…41Plan
- CVE-2019-8271UltraVNC revision 1211 has a heap buffer overflow vulnerability in VNC server code inside file transfer handler, which can potentially…41Plan
Published before and after this one in the same product
- ← EarlierCVE-2026-44040Jul 1, 2026 · UltraVNC vncauth.c uses time-seeded libc rand() to generate VNC authentication challenge bytes26Monitor
- ← EarlierCVE-2026-44041Jul 1, 2026 · UltraVNC vncWc2Mb calls wcslen() before validating that the wide string is NUL-terminated26Monitor
- Later →CVE-2026-7828Jul 1, 2026 · UltraVNC repeater integer overflow in win_log malloc leading to heap overflow21Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
No fix version is recorded for this entry. Check the references for vendor advisories.
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
No history yet (it accumulates with the daily EPSS job).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
- CVE-2026-78310 days apartUltraVNC viewer off-by-one stack overflow in ServerInit desktop name parsing30Monitor
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- none
- Integrity
- none
- Availability
- low · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- None
- Availability impact
- Low
Weakness class (CWE)
CWE-193 · Off-by-one ErrorCVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log
No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.
References
Show all references (2 more)Show less
Vendor advisories and official records. Exploit/PoC links are deliberately left out.