CVE-2021-28041: ssh-agent in OpenSSH before 8.5 has a double free that may be relevant in a few less-common scenarios, such as unconstrained agent-socket ac
Noroxi assessment
Priority: Monitor (action score 29/100)
- 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: 3.5% (FIRST EPSS); higher than 89.2% of all records.
- Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. A user must open a link or visit a page. Special conditions such as timing or configuration are required.
- Fixed version: openssh (Alpine:v3.12) 8.3_p1-r2; openssh (Alpine:v3.13) 8.4_p1-r1; openssh (Alpine:v3.14) 8.5_p1-r0.
- Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).
Low priority for now. Upgrade to openssh (Alpine:v3.12) 8.3_p1-r2; openssh (Alpine:v3.13) 8.4_p1-r1; openssh (Alpine:v3.14) 8.5_p1-r0 or later.
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
ssh-agent in OpenSSH before 8.5 has a double free that may be relevant in a few less-common scenarios, such as unconstrained agent-socket access on a legacy operating system, or the forwarding of an agent to an attacker-controlled host.
- Published
- Mar 5, 2021
- Updated
- Oct 14, 2026
- EPSS
- 3.5% · 89th percentile
- CWE
- CWE-415
Report tools
Action score
29
Monitor
Low priority for now.
- CVSS
- 28 / 40 · 7.1 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 1 / 30 · 3.5%
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi 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 |
|---|---|---|
| openbsd | openssh | cpe:2.3:a:openbsd:openssh |
| fedoraproject | fedora | cpe:2.3:o:fedoraproject:fedora |
| netapp | cloud backup | cpe:2.3:a:netapp:cloud_backup |
| netapp | hci management node | cpe:2.3:a:netapp:hci_management_node |
| netapp | solidfire | cpe:2.3:a:netapp:solidfire |
| netapp | hci compute node firmware | cpe:2.3:o:netapp:hci_compute_node_firmware |
| netapp | hci compute node | cpe:2.3:h:netapp:hci_compute_node |
| netapp | hci storage node firmware | cpe:2.3:o:netapp:hci_storage_node_firmware |
| netapp | hci storage node | cpe:2.3:h:netapp:hci_storage_node |
| oracle | communications offline mediation controller | cpe:2.3:a:oracle:communications_offline_mediation_controller |
| oracle | zfs storage appliance | cpe:2.3:o:oracle:zfs_storage_appliance |
Is OpenSSH on your server exposed to the internet?
The free port scanner finds the open ports on your server and matches the service versions it can read against known vulnerabilities. No account needed.
Run a port scanAffected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- fedoraproject fedora33
- fedoraproject fedora34
- netapp cloud backupall versions
- netapp hci compute node firmwareall versions
- netapp hci management nodeall versions
- netapp hci storage node firmwareall versions
- netapp solidfireall versions
- openbsd openssh8.2 and later · before 8.5
- oracle communications offline mediation controller12.0.0.3.0
- oracle zfs storage appliance8.8
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Alpine:v3.12 | openssh | from 8.2 · before 8.3_p1-r2 | 8.3_p1-r2 |
| Alpine:v3.13 | openssh | from 8.2 · before 8.4_p1-r1 | 8.4_p1-r1 |
| Alpine:v3.14 | openssh | from 8.2 · before 8.5_p1-r0 | 8.5_p1-r0 |
| Debian:12 | openssh | before 1:8.4p1-5 | 1:8.4p1-5 |
| openSUSE:Leap 15.3 | openssh | before 8.4p1-3.9.1 | 8.4p1-3.9.1 |
| openSUSE:Leap 15.3 | openssh-askpass-gnome | before 8.4p1-3.9.1 | 8.4p1-3.9.1 |
| openSUSE:Tumbleweed | openssh | before 9.6p1-3.1 | 9.6p1-3.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP3 | openssh | before 8.4p1-3.9.1 | 8.4p1-3.9.1 |
| SUSE:Linux Enterprise Module for Desktop Applications 15 SP3 | openssh-askpass-gnome | before 8.4p1-3.9.1 | 8.4p1-3.9.1 |
Same product
openbsd: all recordsOther highest-scoring records for the same primary product.
- CVE-2023-38408The PKCS#11 feature in ssh-agent in OpenSSH before 9.3p2 has an insufficiently trustworthy search path, leading to remote code execution if 63This week
- CVE-2018-15473OpenSSH through 7.7 is prone to a user enumeration vulnerability due to not delaying bailout for an invalid authenticating user until after 60This week
- CVE-2016-6210sshd in OpenSSH before 7.3, when SHA256 or SHA512 are used for user password hashing, uses BLOWFISH hashing on a static password when the us60This week
Published before and after this one in the same product
- ← EarlierCVE-2020-14145Jun 29, 2020 · The client side in OpenSSH 5.7 through 8.4 has an Observable Discrepancy leading to an information leak in the algorithm negotiation.24Monitor
- ← EarlierCVE-2020-15778Jul 24, 2020 · scp in OpenSSH through 8.3p1 allows command injection in the scp.c toremote function, as demonstrated by backtick characters in the destinat33Monitor
- Later →CVE-2016-20012Sep 15, 2021 · OpenSSH through 8.7 allows remote attackers, who have a suspicion that a certain combination of username and public key is known to an SSH s23Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| alpine:openssh | 8.3_p1-r2 · Alpine:v3.12 | Package registry (OSV) |
| debian:openssh | 1:8.4p1-5 · Debian:12 | Package registry (OSV) |
| opensuse:openssh | 8.4p1-3.9.1 · openSUSE:Leap 15.3 | Package registry (OSV) |
| opensuse:openssh-askpass-gnome | 8.4p1-3.9.1 · openSUSE:Leap 15.3 | Package registry (OSV) |
| suse:openssh | 8.4p1-3.9.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP3 | Package registry (OSV) |
| suse:openssh-askpass-gnome | 8.4p1-3.9.1 · SUSE:Linux Enterprise Module for Desktop Applications 15 SP3 | Package registry (OSV) |
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.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
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).
National notice (Türkiye Cybersecurity Directorate / USOM)
Official security notices citing this record; remediation advice is on the agency's page.
- TR-21-0989 · Dec 13, 2021(IBM Güvenlik Bildirimi)
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- A low-privileged account is enough.
- A user must open a link or visit a page.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- high · data can be read
- Integrity
- high · data or configuration can be modified
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- Low
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
Weakness class (CWE)
CWE-415 · Double FreeCVSS vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H
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
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (9 more)Show less
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/KQWGII3LQR4AOTPPFXGMTYE7UDEWIUKI/
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TXST2CML2MWY3PNVUXX7FFJE3ATJMNVZ/
- security.gentoo.org/glsa/202105-35
- security.netapp.com/advisory/ntap-20210416-0002/
- www.openssh.com/security.html
- www.openssh.com/txt/release-8.5
- www.openwall.com/lists/oss-security/2021/03/03/1
- www.oracle.com//security-alerts/cpujul2021.html
- cert-portal.siemens.com/productcert/html/ssa-398330.html
Vendor advisories and official records. Exploit/PoC links are deliberately left out.