CVE-2021-27137
An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724.
High
Known exploited
- Severity
- 8.1 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 4.00%
- Chance of exploitation in the next 30 days. Higher than 90.52% of scored vulnerabilities.
- Known exploited
- Yes
- In CISA's catalog since Jul 21, 2026
- Weakness
- CWE-121 Stack-based Buffer Overflow
- Fix
- None yet
- No fixed version published
Exploited in the wild. DD-WRT Stack-Based Buffer Overflow Vulnerability (DD-WRT DD-WRT). Required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines. Due for U.S. federal agencies by Jul 24, 2026.
Description
An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724. An unsafe strcpy in the UPnP handling functionality allows an unauthenticated remote attacker to send a request that would overflow an internal fixed buffer. Exploitation requires the DD-WRT user to enable UPnP (which is off by default, and only listens on internal interfaces by default). This occurs in ssdp_msearch (reachable by an M-SEARCH request).
How to fix
No fixed version has been published yet. Until one is, remove or replace the package, or turn off or isolate the affected feature. This page updates when a fix ships.
Severity breakdown
CVSS 3.1 8.1
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Weakness
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).
How to prevent it
- Operation, Build and Compilation: Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.
- Architecture and Design: Use an abstraction library to abstract away risky APIs. Not a complete solution.
- Implementation: Implement and perform bounds checking on input.
- Implementation: Do not use dangerous functions such as gets. Use safer, equivalent functions which check for boundary errors.
- Operation, Build and Compilation: Run or compile the software using features or extensions that randomly arrange the positions of a program's executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code. Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as "rebasing" (for Windows) and "prelinking" (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking. For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].
References
Advisories
Fixes and patches
Exploits and evidence
Other links
Timeline
- Published
- Added to CISA's Known Exploited Vulnerabilities catalog
- Last updated by the source
- Remediation due for U.S. federal agencies
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-mmjf-rqrv-855v Microsoft Security Advisory CVE-2026-50527 – .NET Denial of Service Vulnerability | High | Same weakness, CWE-121 |
| GHSA-3v45-f3vh-wg7m Oj: Stack Buffer Overflow in Oj.dump via Large Indent | High | Same weakness, CWE-121 |
| CVE-2026-7273 A stack-based buffer overflow vulnerability in the CGI program of Zyxel GS1900-48HPv2 firmware versions through 2.90(ABTQ.1)C0 could allow a LAN-based,… | High Known exploited | Same weakness, CWE-121 |
| GHSA-ghm9-cr32-g9qj rust-openssl: rustMdCtxRef::digest_final() writes past caller buffer with no length check | High | Same weakness, CWE-121 |
| GHSA-98cp-rj9f-6v5g ImageMagick has has a stack-buffer-overflow in MNG encoder with oversized pallete | Medium | Same weakness, CWE-121 |
| GHSA-6588-8gv4-xfgh Microsoft Security Advisory CVE-2026-32203 – .NET and Visual Studio Denial of Service Vulnerability | High | Same weakness, CWE-121 |
| GHSA-8793-7xv6-82cf ImageMagick has an Out-of-bounds Write via InterpretImageFilename | Medium | Same weakness, CWE-121 |
| GHSA-rqq8-jh93-f4vg ImageMagick has stack buffer overflow in MagnifyImage | High | Same weakness, CWE-121 |
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