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Full vulnerability report · 2026
CVE-2026-57166High confidence

PJSIP: Pre-authentication overflow in the telnet CLI error

pjsip · pjproject

6.3MediumCVSS 4.0
Recommended action
Scheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Fix not verified
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-57166 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitypjproject: PJSIP: Denial of Service via malformed telnet CLI command
1 known not affected

The vendor explicitly states that these products are not affected by this CVE.

  • All currently supported Red Hat products
Summary
A flaw was found in PJSIP, a multimedia communication library, specifically in the PJLIB-UTIL telnet command-line interface (CLI) front-end. An unauthenticated remote attacker can exploit a stack buffer overflow by sending a malformed or overly long command line. This vulnerability, present when the telnet CLI is enabled, can lead to application termination, resulting in a Denial of Service (DoS). The impact is limited as access to the unauthenticated CLI is a prerequisite for exploitation.
Remediation
No remediation text is recorded.
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-71660

No EUVD known-exploited evidence

PJSIP is a free and open source multimedia communication library written in C. Prior to commit 4472a31, a stack buffer overflow exists in the PJLIB-UTIL telnet CLI front-end when rendering feedback for an entered command line. Several command-line handling paths write an attacker-influenced amount of data into fixed-size buffers without sufficient bounds checking, so a long command line can overflow them. This affects only applications that enable the telnet CLI front-end (e.g. pj_cli_telnet_create() / --cli-telnet-port). The telnet CLI is an interactive administration interface with no authentication, so any client able to reach it can already issue arbitrary CLI commands. A malformed or overly long command line can overflow a fixed-size stack buffer while rendering command-line feedback, which may lead to application termination. Because reaching this code already requires access to the unauthenticated CLI, the impact beyond that existing access is limited. Applications that do not enable the telnet CLI front-end are not affected. This issue has been patched via commit 4472a31.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
6.3 · CVSS 4.0
Advisory evidence
No linked advisory details stored yet
Recommended actionScheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Fix not verified
01

What, why and how

PJSIP is a free and open source multimedia communication library written in C. Prior to commit 4472a31, a stack buffer overflow exists in the PJLIB-UTIL telnet CLI front-end when rendering feedback for an entered command line. Several command-line handling paths write an attacker-influenced amount of data into fixed-size buffers without sufficient bounds checking, so a long command line can overflow them. This affects only applications that enable the telnet CLI front-end (e.g. pj_cli_telnet_create() / --cli-telnet-port). The telnet CLI is an interactive administration interface with no authentication, so any client able to reach it can already issue arbitrary CLI commands. A malformed or overly long command line can overflow a fixed-size stack buffer while rendering command-line feedback, which may lead to application termination. Because reaching this code already requires access to the unauthenticated CLI, the impact beyond that existing access is limited. Applications that do not enable the telnet CLI front-end are not affected. This issue has been patched via commit 4472a31.

What

PJSIP is a free and open source multimedia communication library written in C. Prior to commit 4472a31, a stack buffer overflow exists in the PJLIB-UTIL telnet CLI front-end when rendering feedback for an entered command line. Several command-line handling paths write an attacker-influenced amount of data into fixed-size buffers without sufficient bounds checking, so a long command line can overflow them. This affects only applications that enable the telnet CLI front-end (e.g. pj_cli_telnet_create() / --cli-telnet-port). The telnet CLI is an interactive administration interface with no authentication, so any client able to reach it can already issue arbitrary CLI commands. A malformed or overly long command line can overflow a fixed-size stack buffer while rendering command-line feedback, which may lead to application termination. Because reaching this code already requires access to the unauthenticated CLI, the impact beyond that existing access is limited. Applications that do not enable the telnet CLI front-end are not affected. This issue has been patched via commit 4472a31.

Why

A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

PJSIP is a free and open source multimedia communication library written in C. Prior to commit 4472a31, a stack buffer overflow exists in the PJLIB-UTIL telnet CLI front-end when rendering feedback for an entered command line. Several command-line handling paths write an attacker-influenced amount of data into fixed-size buffers without sufficient bounds checking, so a long command line can overflow them. This affects only applications that enable the telnet CLI front-end (e.g. pj_cli_telnet_create() / --cli-telnet-port). The telnet CLI is an interactive administration interface with no authentication, so any client able to reach it can already issue arbitrary CLI commands. A malformed or overly long command line can overflow a fixed-size stack buffer while rendering command-line feedback, which may lead to application termination. Because reaching this code already requires access to the unauthenticated CLI, the impact beyond that existing access is limited. Applications that do not enable the telnet CLI front-end are not affected. This issue has been patched via commit 4472a31.

Why

A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Stack-based Buffer Overflow → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Not a CVSS 4.0 base metric
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-121 ↗

CWE-121: Stack-based Buffer Overflow. A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Common Vulnerability Scoring System 4.0: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.ATPresentAttack requirements: A particular deployment or execution condition must be present.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.VCNoneVulnerable-system confidentiality: No direct loss is represented by this metric.VINoneVulnerable-system integrity: No direct loss is represented by this metric.VALowVulnerable-system availability: A successful attack can cause a limited loss.SCNoneSubsequent-system confidentiality: No direct loss is represented by this metric.SINoneSubsequent-system integrity: No direct loss is represented by this metric.SANoneSubsequent-system availability: No direct loss is represented by this metric.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-121
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-71660Official EUVD mapping

PJSIP is a free and open source multimedia communication library written in C. Prior to commit 4472a31, a stack buffer overflow exists in the PJLIB-UTIL telnet CLI front-end when rendering feedback for an entered command line. Several command-line handling paths write an attacker-influenced amount of data into fixed-size buffers without sufficient bounds checking, so a long command line can overflow them. This affects only applications that enable the telnet CLI front-end (e.g. pj_cli_telnet_create() / --cli-telnet-port). The telnet CLI is an interactive administration interface with no authentication, so any client able to reach it can already issue arbitrary CLI commands. A malformed or overly long command line can overflow a fixed-size stack buffer while rendering command-line feedback, which may lead to application termination. Because reaching this code already requires access to the unauthenticated CLI, the impact beyond that existing access is limited. Applications that do not enable the telnet CLI front-end are not affected. This issue has been patched via commit 4472a31.

Official EUVD record
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Fix not verified
Affected
< 4472a31d77a7506ff175dad5abef490f4e31bed1
Fixed
No fixed version is explicitly recorded in the structured CVE data.
Action
No verified patch reference is present in the current structured sources. Check the vendor advisory before making a change.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 4 Sept 2026 · Last source change 4 Sept 2026, 17:12 UTC · CWE-121 · Stack-based Buffer Overflow

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-09-05
European sourceENISA EUVD · EUVD-2026-71660
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD received

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates →
  1. ENISA EUVD mappingEUVD-2026-71660 was added to the official ENISA EUVD mapping for this CVE.
    Before
    not recorded
    After
    {"euvdId":"EUVD-2026-71660"}
    ENISA EUVD ↗
  2. Catalogue recordCVE added to the BlackTree catalogue.
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
ENISA EUVD · EUVD-2026-71660↗Vendor CSAF · Red Hat Product Security↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
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