# ALBA-2021:0556: glibc bug fix and enhancement update

> An attacker can cause slow DNS lookups and potential service degradation via transaction ID collisions in glibc's getaddrinfo function.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Feb 2021

## What is ALBA-2021:0556?

ALBA-2021:0556 is a denial of service vulnerability in glibc-benchtests, published on 16 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The glibc packages provide the standard C libraries (libc), POSIX thread
libraries (libpthread), standard math libraries (libm), and the name
service cache daemon (nscd) used by multiple programs on the system.
Without these libraries, the Linux system cannot function correctly.

Bug Fix(es) and Enhancement(s):

* glibc: Transaction ID collisions cause slow DNS lookups in getaddrinfo
(BZ#1904153)

* glibc: memcpy calls are slower for AMD processors on AlmaLinux 8 than AlmaLinux 7
(BZ#1913750)

## Which versions are affected by ALBA-2021:0556?


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `glibc-benchtests` | AlmaLinux:8 | All versions | 2.28-127.el8_3.2 |
| `glibc-nss-devel` | AlmaLinux:8 | All versions | 2.28-127.el8_3.2 |
| `glibc-static` | AlmaLinux:8 | All versions | 2.28-127.el8_3.2 |
| `nss_hesiod` | AlmaLinux:8 | All versions | 2.28-127.el8_3.2 |

## How do I fix ALBA-2021:0556?

Apply the vendor's patch.

## Is ALBA-2021:0556 being exploited?

There is no known exploitation of ALBA-2021:0556 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for ALBA-2021:0556 and fix it if it is affected.

What it is: ALBA-2021:0556 is a denial of service vulnerability in glibc-benchtests, published on 16 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of ALBA-2021:0556 in the wild and no public exploit code.

Affected product: glibc-benchtests. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/ALBA-2021-0556/ (Markdown: https://insights.sbomify.com/ALBA-2021-0556/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/ALBA-2021:0556

---
From sbomify Insights: https://insights.sbomify.com/ALBA-2021-0556/
Summaries are generated and may contain mistakes; the official description above is the record.