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CVE-2021-39517

21
FAUCET Score

CVE-2021-39517 describes a NULL pointer dereference vulnerability in libjpeg versions through 2020021, specifically within the BlockBitmapRequester::ReconstructUnsampled() function. This flaw allows an unauthenticated attacker to trigger a Denial of Service (DoS) by enticing a user to process a specially crafted JPEG file. With a CVSS score of 6.5 (Medium), the vulnerability is easily exploitable over a network with low attack complexity, leading to high availability impact. Currently, there is no evidence of active exploitation, public exploit code, or significant community discussion surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
<= 2020021CPE matchmatch criteria
cpe:2.3:a:jpeg:libjpeg:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

6.5MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
2.8
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.86%
Probability of exploitation in next 30 days
EPSS Percentile
54.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0086 is in the 65th percentile among its peer group of 26,236 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.1 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

github_advisorypatch availablevia nvd_reference
View patch

References

github.com / thorfdbg/libjpeg/issues/33
ExploitIssue TrackingPatchThird Party Advisory